containers 0.6.5.1

Bug fixes

• foldr' and foldl' for Map and Set are now strict everywhere they
  should be, and we have detailed tests to make sure they stay that way.
  (Thanks, coot.)

• The Ord IntSet instance, which was broken in 0.6.3.1, has been
  repaired.

New instance

• We now have Ord a => Ord (Tree a) (Thanks, Ericson2314.)

Testing fixes

• Thanks to konsumlamm and infinity0 for various bug fixes in the test suite.