This is necessary so Gemnesium will be green.
The original commit came from @amazonwebservices and @trevorrowe in #579. I had to revise the commit and make sure all the test cases are passing. All credits still goes to those guys, thanks a lot!
This test will generate a basic Rails application, include Paperclip into Gemfile, and call basic `has_attached_file` in the model. This will make sure that we're not messing up any of the configuration and integration for our gem and the Rails framework.
(cherry picked from commit e053805)