Lots of changes related to framebuffer/window buffer resizing. Basically,

Lots of changes related to framebuffer/window buffer resizing.  Basically,
instead of passing a GLcontext* to ResizeBuffers(), pass a GLframebuffer*.
The idea is that a window can be resized without it being bound to a rendering
context.  This makes for a nice clean-up in the XFree86 server-side GLX code.
Renamed ctx->Driver.ResizeBuffersMESA() to ctx->Driver.ResizeBuffers().