Changes to ghc

Changes to ghc:
commit 5a963b8238cb52cb1e5bfcfae7f467cd00c171a0
Author: Edward Z. Yang <ezyang@cs.stanford.edu>
Date:   Wed Jul 2 18:27:17 2014 +0100

    Minor edits to Backpack design doc

    Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>