diff --git a/acinclude.m4 b/acinclude.m4
index 9e46179f..dcbe5681 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -6,19 +6,25 @@ dnl
 AC_DEFUN([wi_EXTRA_IDIR], [
 incdir="$1"
 if test -r $incdir ; then
-	case "$CPPFLAGS" in
-		*-I${incdir}*)
-			# echo "   + already had $incdir" 1>&6
-			;;
-		*)
-			if test "$CPPFLAGS" = "" ; then
-				CPPFLAGS="-I$incdir"
-			else
-				CPPFLAGS="$CPPFLAGS -I$incdir"
-			fi
-			echo "   + found $incdir" 1>&6
-			;;
-	esac
+    already=""
+    for CPPflag in $CPPFLAGS ; do
+	if test  "_$CPPflag" = "_-I${incdir}" ; then 
+            already=yes
+            break
+        fi
+    done
+    if test -n "$already" ; then
+        echo "   + already had -I$incdir" 1>&AS_MESSAGE_LOG_FD
+    else
+        if test "$CPPFLAGS" = "" ; then
+                CPPFLAGS="-I$incdir"
+        else
+                CPPFLAGS="$CPPFLAGS -I$incdir"
+        fi
+        echo "   + added -I$incdir" 1>&AS_MESSAGE_LOG_FD
+    fi
+else 
+    echo "   + IDIR is not accessible: '$myincdir'" 1>&AS_MESSAGE_LOG_FD
 fi
 ])
 dnl
@@ -28,19 +34,25 @@ dnl
 AC_DEFUN([wi_EXTRA_LDIR], [
 mylibdir="$1"
 if test -r $mylibdir ; then
-	case "$LDFLAGS" in
-		*-L${mylibdir}*)
-			# echo "   + already had $mylibdir" 1>&6
-			;;
-		*)
-			if test "$LDFLAGS" = "" ; then
-				LDFLAGS="-L$mylibdir"
-			else
-				LDFLAGS="$LDFLAGS -L$mylibdir"
-			fi
-			echo "   + found $mylibdir" 1>&6
-			;;
-	esac
+    already=""
+    for LDflag in $LDFLAGS ; do
+	if test  "_$LDflag" = "_-L${mylibdir}" ; then 
+            already=yes
+            break
+        fi
+    done
+    if test -n "$already" ; then
+        echo "   + already had -L$mylibdir" 1>&AS_MESSAGE_LOG_FD
+    else
+        if test "$LDFLAGS" = "" ; then
+                LDFLAGS="-L$mylibdir"
+        else
+                LDFLAGS="$LDFLAGS -L$mylibdir"
+        fi
+        echo "   + added -L$mylibdir" 1>&AS_MESSAGE_LOG_FD
+    fi
+else 
+    echo "   + LDIR is not accessible: '$mylibdir'" 1>&AS_MESSAGE_LOG_FD
 fi
 ])
 dnl
@@ -50,12 +62,9 @@ dnl
 AC_DEFUN([wi_EXTRA_PDIR], [
 progdir="$1"
 if test -r $progdir ; then
-	case "$PATH" in
-		*:${progdir}*)
-			# echo "   + already had $progdir" 1>&6
-			;;
-		*${progdir}:*)
-			# echo "   + already had $progdir" 1>&6
+	case ":$PATH:" in
+		*:${progdir}:*)
+			echo "   + already had $progdir in \$PATH" 1>&AS_MESSAGE_LOG_FD
 			;;
 		*)
 			if test "$PATH" = "" ; then
@@ -63,9 +72,11 @@ if test -r $progdir ; then
 			else
 				PATH="$PATH:$progdir"
 			fi
-			echo "   + found $progdir" 1>&6
+			echo "   + appended $progdir to \$PATH" 1>&AS_MESSAGE_LOG_FD
 			;;
 	esac
+else 
+       echo "   + PDIR is not accessible: '$progdir'" 1>&AS_MESSAGE_LOG_FD
 fi
 ])
 dnl
@@ -89,23 +100,32 @@ if test "$subexdirs" = "" ; then
 	subexdirs="-"
 fi
 for subexdir in $subexdirs ; do
-if test "$subexdir" = "-" ; then
-	subexdir=""
-else
-	subexdir="/$subexdir"
-fi
-for exdir in $exdirs ; do
-	if test "$exdir" != "/usr" || test "$subexdir" != ""; then
-		incdir="${exdir}/include${subexdir}"
-		wi_EXTRA_IDIR($incdir)
+    if test "$subexdir" = "-" ; then
+            subexdir=""
+    else
+            subexdir="/$subexdir"
+    fi
+    for exdir in $exdirs ; do
+        if test "$exdir" != "/usr" || test "$subexdir" != ""; then
+            incdir="${exdir}/include${subexdir}"
+            wi_EXTRA_IDIR($incdir)
 
-		mylibdir="${exdir}/lib${subexdir}"
-		wi_EXTRA_LDIR($mylibdir)
+dnl On 64-bit machines, if lib64/ exists and is not identical to lib/
+dnl then it should be listed here, listed ahead of lib/.
+            mylibdir64="${exdir}/lib64${subexdir}"
+            mylibdir32="${exdir}/lib${subexdir}"
 
-		progdir="${exdir}/bin${subexdir}"
-		wi_EXTRA_PDIR($progdir)
-	fi
-done
+            if test "x86_64" = $(uname -m) \
+              -a ! ${mylibdir64} -ef ${mylibdir32} ; then
+                wi_EXTRA_LDIR($mylibdir64)
+            fi
+
+            wi_EXTRA_LDIR($mylibdir32)
+
+            progdir="${exdir}/bin${subexdir}"
+            wi_EXTRA_PDIR($progdir)
+        fi
+    done
 done
 ])
 dnl
diff --git a/configure.ac b/configure.ac
index 6ac0c87b..38ae49f5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -437,11 +437,18 @@ esac
 AM_CONDITIONAL(HAVE_FRAMEWORK_PLIB, test "x$ac_cv_framework_PLIB" != "x")
 
 AC_CHECK_HEADER(plib/ul.h)
-if test "x$ac_cv_header_plib_ul_h" != "xyes"; then
+
+AC_CHECK_LIB(plibul,ulInit)
+if test "x$ac_cv_header_plib_ul_h" != "xyes" \
+  -o "x$ac_cv_lib_plibul_ulInit" != "xyes" ; then
     echo
     echo "You *must* have the plib library installed on your system to build"
     echo "SimGear!"
     echo
+    echo "     LIBS: '$LIBS'"
+    echo "  LDFLAGS: '$LDFLAGS'"
+    echo " CPPFLAGS: '$CPPFLAGS'"
+    echo
     echo "Please see README.plib for more details."
     echo
     echo "configure aborted."
@@ -475,18 +482,18 @@ LIBS="$saved_LIBS"
 case "${host}" in
 *-apple-darwin*)
     if test "x$with_osg_framework" != "x"; then
-        AC_CHECK_FRAMEWORK(osgViewer, [#include <osgViewer/Version>], $with_osg_framework)
-        AC_CHECK_FRAMEWORK(osgGA, [#include <osgGA/Version>], $with_osg_framework)
-        AC_CHECK_FRAMEWORK(osgText, [#include <osgText/Version>], $with_osg_framework)
-        AC_CHECK_FRAMEWORK(osgFX, [#include <osgFX/AnisotropicLighting>], $with_osg_framework)
-        AC_CHECK_FRAMEWORK(osgUtil, [#include <osgUtil/Version>], $with_osg_framework)
-        AC_CHECK_FRAMEWORK(osgDB, [#include <osgDB/Version>], $with_osg_framework)
-        AC_CHECK_FRAMEWORK(osgSim, [#include <osgSim/Version>], $with_osg_framework)
-        AC_CHECK_FRAMEWORK(osgParticle, [#include <osgParticle/Version>], $with_osg_framework)
-        AC_CHECK_FRAMEWORK(osg, [#include <osg/Version>], $with_osg_framework)
-        osg_FRAMEWORKS="$FRAMEWORKS"
-        FRAMEWORKS=""
-        AC_SUBST(osg_FRAMEWORKS)
+#       AC_CHECK_FRAMEWORK(osgViewer, [#include <osgViewer/Version>], $with_osg_framework)
+#       AC_CHECK_FRAMEWORK(osgGA, [#include <osgGA/Version>], $with_osg_framework)
+#       AC_CHECK_FRAMEWORK(osgText, [#include <osgText/Version>], $with_osg_framework)
+#       AC_CHECK_FRAMEWORK(osgFX, [#include <osgFX/AnisotropicLighting>], $with_osg_framework)
+#       AC_CHECK_FRAMEWORK(osgUtil, [#include <osgUtil/Version>], $with_osg_framework)
+#       AC_CHECK_FRAMEWORK(osgDB, [#include <osgDB/Version>], $with_osg_framework)
+#       AC_CHECK_FRAMEWORK(osgSim, [#include <osgSim/Version>], $with_osg_framework)
+#       AC_CHECK_FRAMEWORK(osgParticle, [#include <osgParticle/Version>], $with_osg_framework)
+#       AC_CHECK_FRAMEWORK(osg, [#include <osg/Version>], $with_osg_framework)
+#       osg_FRAMEWORKS="$FRAMEWORKS"
+#       FRAMEWORKS=""
+#       AC_SUBST(osg_FRAMEWORKS)
         AC_CHECK_FRAMEWORK(OpenThreads, [#include <OpenThreads/Version>], $with_osg_framework)
         openthreads_FRAMEWORK="$FRAMEWORKS"
         FRAMEWORKS=""
@@ -496,18 +503,33 @@ case "${host}" in
         dnl This is needed when osg dynamic libs are specified 
         dnl instead of OSG frameworks on Mac OS X
         dnl
-        LDFLAGS="$LDFLAGS -L$with_osg"
+        AC_CHECK_LIB(OpenThreads,OpenThreadsGetVersion)
+    fi
+    ;;
+*)
+    if test "x$enable_osgdebug" = "xyes"; then
+        AC_CHECK_LIB(OpenThreadsd,OpenThreadsGetVersion)
+    else
+        AC_CHECK_LIB(OpenThreads,OpenThreadsGetVersion)
     fi
     ;;
 esac
+
 AM_CONDITIONAL(HAVE_FRAMEWORK_OSG, test "x$ac_cv_framework_osg" != "x")
 
 AC_CHECK_HEADER(osg/Version)
-if test "x$ac_cv_header_osg_Version" != "xyes"; then
+
+if test "x$ac_cv_header_osg_Version" != "xyes" -o "x$ac_cv_lib_OpenThreads_OpenThreadsGetVersion" != "xyes"; then
   if test "x$ac_cv_framework_osg" != "xyes"; then
     echo
-    echo "You *must* have the OpenSceneGraph support library installed on your system"
+    echo "You *must* have the OpenThreads library installed on your system"
     echo "to build this version of SimGear!"
+    echo "   Maybe you need to specify --with-osg=DIR."
+    echo "   Maybe you need to specify some LDFLAGS to help the linker."
+    echo
+    echo "     LIBS: '$LIBS'"
+    echo "  LDFLAGS: '$LDFLAGS'"
+    echo " CPPFLAGS: '$CPPFLAGS'"
     echo
     echo "Please see README.OSG for more details."
     echo
@@ -522,6 +544,10 @@ if test "x$ac_cv_header_boost_version_hpp" != "xyes"; then
     echo "You *must* have the Boost library installed on your system"
     echo "to build this version of SimGear!"
     echo
+    echo "     LIBS: '$LIBS'"
+    echo "  LDFLAGS: '$LDFLAGS'"
+    echo " CPPFLAGS: '$CPPFLAGS'"
+    echo
     echo "configure aborted."
     exit
 fi
diff --git a/simgear/props/Makefile.am b/simgear/props/Makefile.am
index acf52017..658fe126 100644
--- a/simgear/props/Makefile.am
+++ b/simgear/props/Makefile.am
@@ -15,7 +15,7 @@ libsgprops_a_SOURCES = \
 	props_io.cxx \
 	AtomicChangeListener.cxx
 
-noinst_PROGRAMS = props_test
+check_PROGRAMS = props_test
 
 props_test_SOURCES = props_test.cxx
 props_test_LDADD = \
diff --git a/simgear/screen/extensions.cxx b/simgear/screen/extensions.cxx
index 7429c0f5..130673c5 100644
--- a/simgear/screen/extensions.cxx
+++ b/simgear/screen/extensions.cxx
@@ -121,11 +121,7 @@ void *SGGetGLProcAddress(const char *func) {
         libHandle = dlopen(NULL, RTLD_LAZY);
 
         if (!libHandle) {
-#if defined (__FreeBSD__)
             const char *error = dlerror();
-#else
-            char *error = dlerror();
-#endif
             if (error) {
                 SG_LOG(SG_GENERAL, SG_INFO, error);
                 return 0;
@@ -145,11 +141,7 @@ void *SGGetGLProcAddress(const char *func) {
     } else if (libHandle != NULL) {
         fptr = dlsym(libHandle, func);
 
-#if defined (__FreeBSD__)
         const char *error = dlerror();
-#else
-        char *error = dlerror();
-#endif
         if (error)
             SG_LOG(SG_GENERAL, SG_INFO, error);
     }