Changes to base

Changes to base:
commit 826f3bddabdc9c3287cb6d91349427890acdc8f3
Author: Herbert Valerio Riedel <hvr@gnu.org>
Date:   Wed Jan 29 22:05:47 2014 +0100

    Improve Haddock markup in `Control.Concurrent.MVar`

    This adds a labeled hyperlink to the Concurrent Haskell paper, and
    replaces the itemized-list headings with proper section
    headings (available since Haddock-2.14).

    Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>