xinerama noPanoramiXExtension

[Dave Airlie]

So we have this wierd situation where certain things test
noPanoramiXExtension in the tree and it changes value after it has
tested them..

So if you run X +xinerama, DRI won't initialise however once the
panoramix extension module initialises it checks if only one screen is
setup and reverts to noPanoramiXExtension = TRUE.

This is very inconsistent from a coding POV, with one half of init
thinking it enabled and later parts thinking it is disabled..
confusion ensues..

Dave.