Catch up with Form API changes in Django SVN

Review Request #138 — Created Aug. 7, 2007 and submitted


Review Board SVN (deprecated)


In Django SVN r5819, they changed the way that forms deal with uploaded files.  This patch updates Review Board to use the new style.

This change is not backwards-compatible with prior Django revisions.
I manually tried submitting a new diff, updating the diff, and uploading a screenshot.  The JSON interface is the only affected codepath that I didn't try myself.