ATI is violating the GLX specs. When a extension is listed in the client GLX list it means that libGL.so implements the extension (this doesn't mean that you can use it on a card), when it is in the server list it means that libglx.so (Xorg library) can support the extension. When both support an extension, the extension should be listed in the overall extension list. When that is not the case applications can't expect such an extension to be around and shouldn't use it. ATI needs to fix their drivers and then our pbuffer code will work fine.
