POST requests were claiming request.method == 'PUT'

So, changed handlers to look for either value.

There were already unit tests which didn't fail tho; so, rewriting happened someplace outside of django unit test encapsulation of .post..

Fixing https://edx-wiki.atlassian.net/browse/STUD-441, https://edx-wiki.atlassian.net/browse/STUD-471

@cdodge @peter-fogg please review