Added osg::BufferObject and a made a number associated to accomodate this

new class. osg::BufferObject wraps up OpenGL pixel and array buffer objects.
Currently implementation is work in progress.

src/osg/Drawable.cpp

@@ -497,7 +497,7 @@ void Drawable::setUpdateCallback(UpdateCallback* ac)
     }
 }
 
-struct ComputeBound : public Drawable::PrimitiveFunctor
+struct ComputeBound : public PrimitiveFunctor
 {
         ComputeBound():_vertices(0) {}