aq1018/mongoid-history — pull request #54 by vecio (2013-01-10 12:09:26+00:00)
Title: Add index support

The $elemMatch selector won't use multiKey index.

For [issue#45](https://github.com/aq1018/mongoid-history/pull/45), Ruby 1.9 is now more popular than 1.8, so we shouldn't
sacrify performance for it. If we want to support 1.8, consider
OrderedHash from ActiveSupport