I did a diff between stable 1.9.0 and tests-passed 2.0 beta1, which should be pretty much the same, and I found three more differences which should not be there.
https://github.com/discourse/discourse/blob/stable/lib/validators/upload_url_validator.rb#L6
https://github.com/discourse/discourse/blob/master/lib/validators/upload_url_validator.rb#L6
https://github.com/discourse/discourse/blame/stable/lib/final_destination.rb#L208-L223
https://github.com/discourse/discourse/blame/v2.0.0.beta1/lib/final_destination.rb#L208-L218