pry-debugger doesn't compile on JRuby, and we're really only using that
locally.

This also removes Pry.

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.

Update Gemfile to make sure we can run the test locally, and also upgrade Rails 3.1 beta to latest version