Fixing destroy callback to delete files just when model destroy method was completed successfully (i.e. no exception like 'foreign key constraint violations' was raised)

When testing if post_processing is set, the method should be used. This allows plugins to overwrite the post_processing decision. This is useful for plugins that want to do the post_processing in a background processor.

An implemenation of the watermark processor alluded to is in this gist
https://gist.github.com/1171081

Decouple the Interpolations class from the Attachment classs, you can extend Paperclip with custom interpolations as paperclip-extended does.

Abstract out the file geometry parser within Thumbnail. This makes it possible to have different cropping and scaling controls, as the papermill gem does.

Conflicts:
	lib/paperclip/upfile.rb
	paperclip.gemspec

This will prevent someone to think that Paperclip test suite for master branch is currently failing, as the build was failed on a WIP branch, not the main branch.

http://travis-ci.org/#!/thoughtbot/paperclip/builds.

I think it's OK to have the bugfix for MongoDB in the plugin.

This reverts commit cde22564.

Add rubinius to travis testing

Bump rails 3_1 version to rc6

This reverts commit fe01ae69.

It seems like that JRuby on travis-ci is broken[1], so we shouldn't test against it to reduce the false-positive result. I've run the test locally, and it passed just fine[2].

[1]: http://travis-ci.org/#!/thoughtbot/paperclip/builds/79181
[2]: https://gist.github.com/299686b412f9ad878e16

Update Gemfile to make sure we can run the test locally, and also upgrade Rails 3.1 beta to latest version