Pull request - 11/10/14

This is a good candidate for a spec. Hopefully it would be fairly quick to write a failing test that creates duplicate ingredients. As for preventing that duplication, I think the easiest way would be adding a [uniqueness validation](http://guides.rubyonrails.org/active_record_validations.html#uniqueness) to the `Ingredient` class. However, if you want to be really certain that ingredients aren't duplicated, you'll also need to add a [unique index](http://robots.thoughtbot.com/the-perils-of-uniqueness-validations).