Added a fix for a multi-threading bug that occured when TerrainTiles were accessed via the Terrain::_updateTerrainTileSet that were being deleted at the same time by the DatabasePager thread.
Added a fix for a multi-threading bug that occured when TerrainTiles were accessed via the Terrain::_updateTerrainTileSet that were being deleted at the same time by the DatabasePager thread.


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