Bug#500887: xserver-xorg: Unpredictable X server crash when Gnome screen saver (lock screen) run

[Jason White <jason@jasonjgw.net>]

This time I managed to reproduce the real culprit. The exact sequence of steps
isn't clear: working in Gnome and Iceweasel for a while, then selecting "Lock
screen" from the Gnome system menu did the trick.

The backtrace from gdb follows.

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7f501ebdc6e0 (LWP 17615)]
0x0000000000000061 in ?? ()
(gdb) bt
#0  0x0000000000000061 in ?? ()
#1  0x00007f501c157a20 in DoSwapInterval (cl=<value optimized out>, 
    pc=0x2d5c674 "\217\020\004", do_swap=0)
    at ../../../GL/glx/swap_interval.c:80
#2  0x00007f501c135732 in __glXDisp_VendorPrivate (cl=0x19c50a0, 
    pc=0x2d5c674 "\217\020\004") at ../../../GL/glx/glxcmds.c:2328
#3  0x00007f501c1398a5 in __glXDispatch (client=0x19b6210)
    at ../../../GL/glx/glxext.c:561
#4  0x000000000044f7d2 in Dispatch () at ../../dix/dispatch.c:502
#5  0x0000000000436bd5 in main (argc=3, argv=0x7fff26bfb928, 
    envp=<value optimized out>) at ../../dix/main.c:452
(gdb) quit