Modify a draft when using update_from_changenum

Review Request #213 — Created Jan. 25, 2008 and submitted — Latest diff uploaded

Review Board SVN (deprecated)
Our code for updating a review request by changenum through the API was still operating on the review request and not the draft. This meant that a subsequent call to post-review would touch the underlying review request that everyone saw, but not the draft that the user was modifying. Now we update the draft.
Tested this by creating a review request with a changenum. Saw that the initial review request creation still worked and the changeset info was still being pulled. I then updated the content and ran post-review again. The draft content had changed to match.