Introduced OSG_GL*_FEATURES macros defined in include/GL that are set to 0 or 1 according to what the assocoated version of GL is compiled against.

Removed EXT postfix of FrameBufferObject functions, and added support for checking non EXT versions frame buffer object GL functions.

Introduced usage of OSG_GL*_FEATURES to avoid some #if #else #endif code blocks.

Using a submissions from Paul Martz as a guide added perliminary GL3 support to a range of OSG classes

include/osg/GL

@@ -162,4 +162,35 @@
     #define GL_LUMINANCE_ALPHA                0x190A
 #endif
 
+#ifdef OSG_GL1_AVAILABLE
+    #define OSG_GL1_FEATURES 1
+#else 
+    #define OSG_GL1_FEATURES 0
+#endif
+
+#ifdef OSG_GL2_AVAILABLE
+    #define OSG_GL2_FEATURES 1
+#else 
+    #define OSG_GL2_FEATURES 0
+#endif
+
+#ifdef OSG_GL3_AVAILABLE
+    #define OSG_GL3_FEATURES 1
+#else 
+    #define OSG_GL3_FEATURES 0
+#endif
+
+#ifdef OSG_GLES1_AVAILABLE
+    #define OSG_GLES1_FEATURES 1
+#else 
+    #define OSG_GLES1_FEATURES 0
+#endif
+
+#ifdef OSG_GLES2_AVAILABLE
+    #define OSG_GLES2_FEATURES 1
+#else 
+    #define OSG_GLES2_FEATURES 0
+#endif
+
+
 #endif  // __osgGL_h