Added a few more comments on the DeleteHandler.
Added a few more comments on the DeleteHandler.

Changed the friend struct DeleteHandler to friend class DeleteHandler.


XiaoCC/osg,omega-hub/osg,artoolkit/osg,stmh/osg,ntoand/osg,omega-hub/osg,omega-hub/osg,ghub/osg,ntoand/osg,artoolkit/osg,artoolkit/osg,stmh/osg,XiaoCC/osg,ghub/osg,artoolkit/osg,ntoand/osg,stmh/osg,koshman86/osg,XiaoCC/osg,ghub/osg,stmh/osg,ghub/osg,XiaoCC/osg,XiaoCC/osg,omega-hub/osg,koshman86/osg,ntoand/osg,stmh/osg,koshman86/osg,koshman86/osg