Changes to ghc

Changes to ghc:
commit ec38f4abd90ec6008aea8214c04a6af4be6814f8
Author: Edward Z. Yang <ezyang@cs.stanford.edu>
Date:   Thu Jun 26 14:40:45 2014 +0100

    Minor updates to Backpack docs.

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