Add missing description args to the review_request_closed signal.
Review Request #8037 — Created March 7, 2016 and submitted
Unlike the review_request_closing signal, the review_request_closed signal didn't have arguments indicating the close description or the rich text flag. This adds and documents those arguments.
Tested this with an extension that needed these arguments.
Tool: Pyflakes Processed Files: reviewboard/reviews/signals.py reviewboard/reviews/models/review_request.py Tool: PEP8 Style Checker Processed Files: reviewboard/reviews/signals.py reviewboard/reviews/models/review_request.py