Changes to ghc

Changes to ghc:
commit 41cfc96b55a4a44953fc20aa72ef50789ba6ceab
Author: Krzysztof Gogolewski <krz.gogolewski@gmail.com>
Date:   Thu Feb 6 23:15:50 2014 +0100

    Tweak documentation of monomorphism restriction

    Suggested by Gabor Greif on ghc-devs