Make Travis test against ActiveRecord 3.2, 4.0, and 4.1
only run the test if  defined?(ActiveRecord::Migration::CommandRecorder)
more obvious skip when revert isn't defined
added support for 3.0 and 3.1. We don't need to run the tests with 1.9.3 AND 2.0.0.
Merge pull request #135 from mceachen/ci_support

Make Travis test against ActiveRecord 3.2, 4.0, and 4.1