When creating and using an appgroup, its possible to crash the Xserver.
The problem occurs when the appgroup leader exits.
This should cause all applications in the appgroup to exit.
Due to a coding error in Xext/appgroup.c, some applications are left open.
When the windows associated with applications are closed after the application
group leader exits, the Xserver crashes, SIGSEGV, while using an invalid pointer.
Test case, and patch attached.
Created attachment 5657 [details]
Created attachment 5658 [details] [review]
committed to HEAD, thanks