Changes to ghc

Changes to ghc:
commit 54e655536ecf7eba755b334058d5c22dab251bea
Author: Simon Peyton Jones <simonpj@microsoft.com>
Date:   Mon Apr 7 15:45:35 2014 +0100

    Derive Typable for promoted data constructors (Trac #8950)

    I got sucked into a significant refactoring of the way that
    Typeable instances are derived.  This makes it simpler and
    more uniform.

    I also improved the documentation in the user manual.  Typeable
    really is different to other classes, and now gets its own subsection.