It seems that GHC 6.6 just enables -fglasgow-exts when it sees any LANGUAGE
pragma, so not all of them were added; this patch adds the rest of them, which
is necessary for xmonad to compile in GHC >=6.7.
This works nicely for describing a fixed xinerama-like layout.
(e.g. when using two distinct VNC clients to log into a single
VNC server and attain multiheadedness).
This modifies all the contrib modules to work (so far as I know) with the
new contrib layout. The exception is the LayoutHooks module, which isn't
used. It exports an API that is inherently unsafe, so far as I can tell
(and always has been).