Correctly check for PBuffer support even if FBO is supported in GL rendersystem
Correctly check for PBuffer support even if FBO is supported in GL rendersystem

--HG--
branch : v1-7

ruleless/ogre,ruleless/ogre,bhlzlx/ogre,bhlzlx/ogre,ruleless/ogre,ehsan/ogre,ruleless/ogre,ehsan/ogre,ruleless/ogre,bhlzlx/ogre,ehsan/ogre,ehsan/ogre,bhlzlx/ogre,ruleless/ogre,bhlzlx/ogre,bhlzlx/ogre,ehsan/ogre