please test: Xlib/XCB fixes

[Brian Paul]

Jamey Sharp wrote:
> Josh and I sorted out a bunch of Xlib bugs this week, especially in
> support for multi-threaded applications. I'm embarrassed that I hadn't
> realized the thread support was so bad--but there are so few threaded
> Xlib apps, and even fewer that are open source.

This sounds great.  Writing threaded GL apps has been a challenge 
because of threading bugs in Xlib.

If you have a Mesa tree built, try progs/xdemos/glthreads.  If you use 
a software renderer (swrast or softpipe) you'll be drawing everything 
through Xlib.

-Brian