make everything work with new doLayout.

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).

TwoPane.hs

@@ -35,7 +35,7 @@ import StackSet ( focus, up, down)
 -- > twoPane defaultDelta (1%2)
 
 twoPane :: Rational -> Rational -> Layout a
-twoPane delta split = Layout { doLayout = \r s -> return $ arrange r s, modifyLayout = message }
+twoPane delta split = Layout { doLayout = \r s -> return (arrange r s,Nothing), modifyLayout = message }
  where
     arrange rect st = case reverse (up st) of
                         (master:_) -> [(master,left),(focus st,right)]