Needs work for S3 Attachments.

The new default :path and :include include the name of the model and
also nests the model ID under a series of subdirectories, improving
filesystem access speed when more than 1024 models have saved
attachments.

The easiest way to upgrade is to add an explicit :url and :path to your
has_attached_file calls:

    has_attached_file :avatar,
      :path => ":rails_root/public/system/:attachment/:id/:style/:filename",
      :url => "/system/:attachment/:id/:style/:filename"

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 will fix the problem on the CI server, where some time the change occurred by "write_file" will not trigger Rubinius to generate a compiled .rbc file.

Closes #602

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.