Add an 'add(str)' function that adds a search path separator and appends the str.

simgear/misc/sg_path.cxx

@@ -112,6 +112,11 @@ void SGPath::append( const string& p ) {
     fix();
 }
 
+//add a new path component to the existing path string
+void SGPath::add( const string& p ) {
+    append( sgSearchPathSep+p );
+}
+
 
 // concatenate a string to the end of the path without inserting a
 // path separator

simgear/misc/sg_path.hxx

@@ -79,6 +79,12 @@ public:
      * @param p additional path component */
     void append( const string& p );
 
+    /**
+     * Append a new piece to the existing path.  Inserts a search path
+     * separator to the existing path and the new patch component.
+     * @param p additional path component */
+    void add( const string& p );
+
     /**
      * Concatenate a string to the end of the path without inserting a
      * path separator.