allow users to login via AJAX

in order to use backbone.js you need to have your authentication controller accept and respond with json. There are several guides out there but I just picked [this one](http://natashatherobot.com/devise-rails-sign-in/) mainly because it would be easy to link and is just about how I would do it anyway. 

Its a real hassle to try to debug this stuff through the browser so I chose to add a little testing structure for you that will probably give you a nice pattern to follow for your other resources. In my mind [request specs](https://www.relishapp.com/rspec/rspec-rails/docs/request-specs/request-spec) provide the nicest way to test these AJAX resources and have more 'bang for the buck' than controller tests. I tried to get your current tests running in the `test` directory but after about 1/2 hour I quit. I don't like Test::Unit anyway and it appeared these were not your tests but just scaffolded. So I added rspec which is a nicer structure and probably more standard in rails projects these days. I really haven't touched the JS side of the project, since that is what our coding time is for, but these sorts of hangups would prevent us on focusing on what you want to learn and its always a bit of a google fest to get this stuff configured and working correctly.

Sorry I wasn't able to get with you this weekend. Hopefully this provides some goodwill towards my intent to help you.