Added CMake support for specifying what OpenGL target and features that the OpenSceneGraph build should use.

Added use of the new Cmake generated #define's for optionally compiling parts of the OpenSceneGraph's OpenGL support for the various OpenGL targets

src/osg/AlphaFunc.cpp

@@ -29,6 +29,10 @@ AlphaFunc::~AlphaFunc()
 
 void AlphaFunc::apply(State&) const
 {
+#ifdef OSG_GL_FIXED_FUNCTION_AVAILABLE
     glAlphaFunc((GLenum)_comparisonFunc,_referenceValue);
+#else
+    osg::notify(osg::NOTICE)<<"Warning: AlphaFunc::apply(State&) - not supported."<<std::endl;
+#endif
 }