[Xcb] print backtraces in case an assert fails inside xlib/xcb

[Julien Cristau]

On Thu, Jun  7, 2007 at 19:22:31 -0700, Barton C Massey wrote:

> Ah.  Thanks.  Doesn't sound like something we can fix in
> XCB?
> 
Indeed, it's not :)

Cheers,
Julien