Since we require GHC 7.6 it won't hurt to require containers 0.5
and get rid of our copy of it.
See: https://www.haskell.org/platform/changelog.html
1 patch for repository http://darcs.net:
patch 2e5c8af88a08f194b82455e817c1e2eba81f07e0
Author: Guillaume Hoffmann <guillaumh@gmail.com>
Date: Fri Jun 12 12:48:02 ART 2015
* require containers 0.5 and remove local copy of it