The twiddle-wakka specifying only major and minor (not tiny) versions
will grab latest minor, which ended up being 3.2 for all versions of
Rails supported. This ensures that when we report supporting Rails 3.0,
3.1, and 3.2, we actually test against those versions.
It also backports ActiveSupport::Notifications.subscribed, which was
added in 3.2.
Closes#367