Changes to ghc

Changes to ghc:
commit 5bda0d08d8fec86433917b65a93836d2372a5b5c
Author: Krzysztof Gogolewski <krz.gogolewski@gmail.com>
Date:   Wed Feb 5 20:40:13 2014 +0100

    Mention that MR is off by default in GHCi in documentation