[xmonad] darcs patch: Small bugfix to X.L.Fullscreen

When using xmonad on another machine, the XMonad.Layout.Fullscreen module stopped refreshing the layout when a window entered fullscreen. This patch makes the layout modifiers return a Just instead of a Nothing on the FullscreenChanged message, fixing the bug. I do wonder, however, why the modifiers worked fine before. The patch also fixes some funny whitespace. -- Audun Skaugen