Removed the 'using namespace std' and replaced with more specific 'using std::ostream'

this should help prevent polution of the global namespace with std when including
these osg include files.

include/osg/Matrix

@@ -13,7 +13,7 @@
 #include <iostream.h>
 #else
 #include <iostream>
-using namespace std;
+using std::ostream;
 #endif
 
 // temporary #define to keep backwards compatibility.

include/osg/Notify

@@ -13,7 +13,8 @@
 #else
 #include <iostream>
 #include <fstream>
-using namespace std;
+using std::ostream;
+using std::ofstream;
 #endif
 
 

include/osg/Vec2

@@ -11,7 +11,7 @@
 #include <iostream.h>
 #else
 #include <iostream>
-using namespace std;
+using std::ostream;
 #endif
 
 namespace osg {

include/osg/Vec3

@@ -11,7 +11,7 @@
 #include <iostream.h>
 #else
 #include <iostream>
-using namespace std;
+using std::ostream;
 #endif
 
 namespace osg {

include/osg/Vec4

@@ -11,7 +11,7 @@
 #include <iostream.h>
 #else
 #include <iostream>
-using namespace std;
+using std::ostream;
 #endif
 
 namespace osg {