There are bugs that result from having drafts for both a reply to a review
and a review of a diff. These consist of:
* Putting comments into the wrong draft.
* Saving/deleting the wrong draft (note that we create fine).
* Not being able to view the diff viewer when both drafts exist (due to our
Review.objects.get() queries not being specific enough about the
base_reply_to parameter).
We have proper separation in the API (/r/#/reviews/draft/* and
/r/#/reviews/#/replies/draft/*), but we must not be using the right ones at
times.
