[Xmonad] darcs patch: Allow user to override Xinerama detection

[Donald Bruce Stewart]

alec:
> (please ignore previous patch - I forgot to update the README)
> 
> The attached patch allows the user to override Xinerama detection.  I
> have the Xinerama headers installed because Debian's GTK+ development
> packages require it, but I only have one screen; for some reason,
> probably related to the laptop's VGA out, xmonad thinks there's a second
> one and I lose a workspace.  The attached patch allows the user to pass
> the --without-xinerama to configure to manually disable xinerama.
> 
> You'll need to run 'autoreconf'.
> 

Begin able to override misdetection seems reasonably harmless. Checking
the files are in the right place, so autoconf can find them, might also
be warranted here too, Alec.

-- Don