sylvainsf/mongomapper-paperclip — pull request #2 by shevaun (2013-04-08 22:38:32+00:00)
Title: extend ActiveSupport::Concern to support older Rails versions

I haven't tested this on Rails < 3.2, but it does work in 3.2 and hopefully resolves the issues you're seeing in 3.1 - please let me know if it doesn't.