add ewmhDesktopsLayout for EWMH interaction
add ewmhDesktopsLayout for EWMH interaction

This is based on Andrea’s EventHook thingy. Note that I could not merge
this with some of my earlier EWHM interaction patches (darcs was failing on me),
so I copied some code. Do not try to merge it with those patches either.

Note that the docs are saying what should work. There are still some bugs
to be resolved, but it works sometimes and should work similar to what we have.

darcs-hash:20080319195736-23c07-78be594f4352055d21d921eecab4312905124cf9

kmels/xmonad-launcher,kmels/xmonad-launcher