Moved GL2Extensions functionality into the include/osg/GLExtensions header and new GLExtensions object.

Moved the #defines into new include/osg/GLDefines
Converted all GL2Extensions usage to GLExtensions usage


git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk@14593 16af8721-9629-0410-8352-f15c8da7e697

src/osgParticle/PrecipitationEffect.cpp

@@ -838,7 +838,7 @@ void PrecipitationEffect::PrecipitationDrawable::drawImplementation(osg::RenderI
 if (!_geometry) return;
 
 
-    const osg::GL2Extensions* extensions = renderInfo.getState()->get<osg::GL2Extensions>();
+    const osg::GLExtensions* extensions = renderInfo.getState()->get<osg::GLExtensions>();
 
     // save OpenGL matrices
     glPushMatrix();