drisw: Try harder to probe whether MIT-SHM works

XQueryExtension merely tells you whether the extension exists, it doesn't tell you whether you're local enough for it to work. XShmQueryVersion is not enough to discover this either, you need to provoke the server to do actual work, and if it thinks you're remote it will throw BadRequest at you. So send an invalid ShmDetach and use the error code to distinguish local from remote.

Signed-off-by: Adam Jackson ajax@redhat.com