If one sets a viewport to be larger than the actual
window size, and then attempt to draw in the off-window
area, you can crash the X server.
Happens with Mesa in XFree 4.1 and recent CVS 126.96.36.199.
Does not happen with ATI DRI OpenGL for either one.
I've included a bug demo. After the window is drawn,
manualy resize the window down a bit. When the
graphics refreshes, X dies.
I already submitted this to Mesa, but I think it may