Changes to ghc

Changes to ghc:
commit 3abf949b50f9fd84633fbf9b479e9cd5fa7125cd
Author: Joachim Breitner <mail@joachim-breitner.de>
Date:   Sat May 10 11:38:49 2014 +0200

    Require transformers for T5979

    in order to get a reliable error message
    (although the error message could be improved anyways to mention the
    explicit package the module is imported with.)