configure check for Xrandr extension

[Alex Pasadyn]

Lionel Ulmer wrote:
> As proper desktop support is a post-1.0 feature, I would really like to have
> a configuration option, even hidden somewhere :-)

Well it currently does enable RandR based on the option.  And for 
everything I tested desktop mode worked fine for trapping the app 
inside.  I was hoping that whatever bug you're getting in desktop mode 
didn't require the eventual big changes to fix it.

But anyway, if you do turn everything off including desktop mode, you 
will probably want to hack X11DRV_Settings_Init in your tree to return 
additional modes for the "NoRes" case by adding some calls to 
X11DRV_Settings_AddOneMode.  Otherwise you only get one mode that is the 
same size as the X desktop.

Alex