Sandwich new Monad layer GmOutT into transformer stack

This way we can have access to some options pre Cradle setup which
should fix the output interleaving problems I was observing.

Language/Haskell/GhcMod/Debug.hs

@@ -39,7 +39,7 @@ debugInfo = do
               fsep $ map text pkgOpts)
       , "GHC System libraries: " ++ ghcLibDir
       , "GHC user options:\n"    ++ render (nest 4 $
-              fsep $ map text ghcUserOptions)
+              fsep $ map text optGhcUserOptions)
       ] ++ cabal
 
 cabalDebug :: IOish m => GhcModT m [String]