I propose changing the GLContextProvider::CreatePBuffer() API to CreateTexturable(), since pbuffers can't be bound to textures on all platforms. This makes implementing and using Oleg's BindTex/ReleaseTex() API for CGL, WGL, and GLX more natural.

Let's hold off on doing this rename -- it might well become something like CreateOffscreen in the near future, but would like to think about the full API path some. This might end up creating a dummy context with a FBO, which would mean extra info would need to get passed back.

Holding off on CreatePBuffer() rename per comment 1.

All the stuff here is either no longer relevant or subsumed by other work.