Changes to ghc

Changes to ghc:
commit 674c969c240632da70ed2928fa30c20a9a52e5dc
Author: Richard Eisenberg <eir@cis.upenn.edu>
Date:   Sat Feb 8 22:09:12 2014 -0500

    Fix #8631.

    This patch allows turning on ImpredicativeTypes while type-checking
    the code generated by GeneralizedNewtypeDeriving. It does this
    by adding a field ib_extensions to InstBindings, informing the
    type-checker what extensions should be enabled while type-checking
    the instance.