[Mesa-dev] EGL/GLX syncup: XCB for GLX, vblank_mode for EGL.

[Eric Anholt]

We've talked about relying on XCB for GLX in the past, and this brings the two
codebases closer to each other.  I've only XCB-converted portions of
dri2_glx.c to use XCB when the xlib version of the function could be removed
without touching the gallium code.

Still missing is invalidate event support for EGL, so its swapbuffers
(actually glViewport, lol) is higher overhead.

Also available as glx-xcb of my mesa tree.