Closed review requests were having their "submitted at" timestamps updated by

subsequent comments on the request. This led to situations where requests that 

had long since been submitted were updated and erroneously listed as having been 

submitted at time of the most recent comment/activity. This error was caused 

due to the "submitted at" section using the "last updated" field of the 

review request.
The submitted fix involves re-writing the method get_close_description of 

the review request model into a new method get_close_info, which returns a 

python dictionary including the values returned by get_close_description, 

as well as a timestamp indicating when the review request had been closed. 

This timestamp was then used instead of the "last updated" timestamp for 

submitted review requests. get_close_description was also re-written to 

wrap the new get_close_info method, and now raises a deprecation 

warning on use.

Manually tested bug by taking steps to reproduce bug after fix, which no longer 

seems to cause the same issue after applying the patch.
Added a test to ensure that the review request member function get_close_info 

returns a dictionary with the proper keys (including the added timestamp), and 

that closing a review request does cause the timestamp to be created.
Also added a test to ensure that deprecated function get_close_description 

now throws a deprecation warning.