Bitbucket reviews should be able to be made against anything

From the UI, I can't create a Stash review from any commit to any other commit. I have to choose a source branch (or something I've pushed from the command line), and a destination branch or tag only. I'd like to create a review for any source and any destination so we can get a diff to discuss about.

At the moment this can be worked around by pushing two branches (a commit and its parent) and having a review created with these two.