Do you actually need it? Otherwise I think we might as well remove it completely, clearly nobody depends on it since it has been broken for a long time.
Well, sometimes, in some rare debugging cases, it's useful to have it, yeah.
Basically, I was hunting down a GFX corruption bug and was wondering if it was due to the fact that the XShm code path is 'asynchronous' and that we sent two updates in a row while the first one was not yet finished processing on the X server side...
And in doing this, I found out that the 'disable XShm' option did not work anymore and I sent this patch.
Lionel