[Xcb] xcb_wait_for_reply deadlocking with xcb_property_changed call

[Jamey Sharp]

Julien, you re-wrote libxcb-property; does anything about
https://bugs.freedesktop.org/show_bug.cgi?id=27368 sound familiar, or
do you have any advice for Nick? I seem to recall some discussion of
getting rid of the property library entirely; is it still useful?

Nick, I'm not sure you want to be handling events from multiple
threads. XCB should allow you to call xcb_wait_for_event from any
number of threads simultaneously, but I'd argue it isn't a good idea,
because then you have no idea what order the events arrived in. Also,
I don't see any locking in libxcb-property, so while it looks like
calling xcb_property_changed from multiple threads is probably safe, I
wouldn't bet on it.

I can't make any sense of the xtrace, because it's trimmed too far.
I'd like to see at least as many GetProperty requests as you have
threads blocked in libxcb-property. Which, again, should probably not
be more than 1. :-) Perhaps if you gzip the trace it will fit in 1MB?

I'm also hopeful that you can get stack traces with debug symbols. I
don't know why installing the Ubuntu -dbg packages didn't help.

Jamey