Fix close descriptions on older review requests.

The logic for determining the current close description text broke on
older review requests. It assumed that the latest change description was
a status change, but this wouldn't be true for any older ones. It would
happily use the text, which was confusing.

Now the view checks specifically for a proper status change, and passes
the appropriate text as a "close_description" parameter to the template.
The template no longer has to know about the latest change description
when figuring out the text.

Tested this on some older review requests, and on some new ones with
recorded status changes. It was no longer grabbing the wrong text on
old ones, but still got the right text on new ones.