Added more comprehensive releaseGLObjects(State*=0) throughout Nodes,

Drawables,StateSet, and osgDB::Registry.

Added cleanup_frame() from to osgProducer::OsgCamerGroup to help with proper
clean of OpenGL objects before exit, and modified osgviewer, osghangglider,
osgwindows examples to do the extra frame call to cleanup_frame() before exit.

src/osg/Node.cpp

@@ -427,3 +427,11 @@ void Node::dirtyBound()
 
     }
 }
+
+void Node::releaseGLObjects(osg::State* state) const
+{
+    if (_stateset.valid()) _stateset->releaseGLObjects(state);
+}
+
+
+