Add LANGUAGE pragams

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.

WorkspaceDir.hs

@@ -1,4 +1,5 @@
-{-# LANGUAGE FlexibleInstances #-}
+{-# OPTIONS_GHC -fglasgow-exts #-} -- For deriving Data/Typeable
+{-# LANGUAGE FlexibleInstances, MultiParamTypeClasses #-}
 
 -----------------------------------------------------------------------------
 -- |