ActiveRecord 3.2.13.rc1 support

As with ActiveRecord 4.0.0.beta1 support, this pull request is pending the official release of rails 3.2.13, but should help people collaborate on bugs which may have been introduced.

The standalone-migrations remained green, so no changes needed to be made. Re-running standalone migrations on our app also still worked. So far, it looks like a drop-in upgrade from 3.2.12.