Let's keep it as class method, as Rails 3.0.x require migration methods
to be class methods.

This reverts commit 029fe02f.

* Added test for checking if path gets interpolated correctly without passing
  :path or :url options
* gsub default :rails_root filesystem-like path to nothing for Fog storage,
  just like in S3 Storage.

:class interpolates to the plural

`s3_protocol` now returns the protocol without a colon. If you need a
colon, you can pass in `true` as a second argument.

This might not be a best solution, so any better patch that does not
introduce a regression is welcome.

Fixes #921

* Add StyleTokenNotFound in Errors
* Adjust tests to make sure :style present where not currently defined

Now it includes :class and :id_partition

Also, 3.1.0 and 3.1.1 will be yanked because of the regression.

@mvz caught this in 90ea9dab.
Thank you!

This will solve an issue when using Paperclip without Active Record
such as Mongoid.

Fixes #919

This is for Rails 3.1+

Fixes #902