Original commit message from CVS:
* sys/ximage/ximagesink.c: (gst_ximagesink_check_xshm_calls),
(gst_ximagesink_ximage_new):
* sys/xvimage/xvimagesink.c: (gst_xvimagesink_check_xshm_calls),
(gst_xvimagesink_xvimage_new):
Apparently on Solaris and OS/X (at least), it's not legal to ask the
X server to attach to a shared memory segment after we've deleted it,
with the result that MIT-SHM is disabled. Instead, remove it only after
X succeeds in attaching too.