Changes to ghc

Changes to ghc:
commit 235fd88a9a35a6ca1aed70ff71291d7b433e45e4
Author: Austin Seipp <austin@well-typed.com>
Date:   Tue Jan 14 20:16:26 2014 -0600

    Turn -XTypeHoles into a (on by default) warning

    After some discussion on ghc-devs@ and elsewhere, it seemed favorable to
    make this change as type holes don't let any invalid programs though,
    they merely change what the compiler reports in case of certain errors
    (namely unbound occurrences, or _ appearing on a LHS.)

    Now, the warning mechanism is controlled by -f[no-]warn-type-errors,
    just like any other regular warning. Again, on by default.

    The documentation and tests have been updated accordingly.

    Signed-off-by: Austin Seipp <austin@well-typed.com>