Changes to ghc

Changes to ghc:
commit 6ecb89fe88573fe16b2ae4c4c43d11b20ac4492e
Author: Austin Seipp <austin@well-typed.com>
Date:   Mon Apr 7 10:15:05 2014 -0500

    users_guide: note -XPatternSynonyms is required for use sites

    Signed-off-by: Austin Seipp <austin@well-typed.com>
    (cherry picked from commit b059dcc81e9c4097b5f04f85e1ac33586c494110)