New fix for dm-validations 1.2 and Sinatra

I was in need of using the new 1.2 dm-validations features but the already open pull request lacks of the latest changes done by krobertson to dm-paperclip
So I forked the current status of the repo and added the changes donde in the other pull request, then fixed all the tests.

Also I added the commit by inbeom found here: from https://github.com/inbeom/dm-paperclip/commit/c3bb759755dffa8bae0d0d7c1a1ae33160d89dbb to make dm-paperclip compatible with Sinatra

All the credits are for the commit devs, I only fixed the tests that were not passing