Changes to ghc

Changes to ghc:
commit 59cb44a3ee4b25fce6dc19816e9647e92e5ff743
Author: Joachim Breitner <mail@joachim-breitner.de>
Date:   Mon Jan 20 15:16:06 2014 +0000

    Explain why TcAxiomInstCo carries [TcCoercion], and not [TcType]