Changes to ghc

Changes to ghc:
commit 2a41db332d9738198418513fe99abb04a0619928
Author: Edward Z. Yang <ezyang@cs.stanford.edu>
Date:   Wed Jun 18 22:59:23 2014 +0100

    In progress Backpack implementation docs.

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