Non-match on multipart mail body should return nil

This fixes a bug with matching the body of a multipart mail message.
When the body of a multipart mail message was not matched, it defaulted to
the result of the 'message.parts.each' iteration which is the
array of parts - now it will return nil as expected.
Merge pull request #57 from rstawarz/master

Non-match on multipart mail body should return nil
process_maildir now works outside of #run
Merge pull request #60 from johncant/master

Compatability with mailman-rails
Fixed Rails env require bug
Merge pull request #61 from johncant/master

Mailman.config.rails_root false bug fix