rfcbot is missing non-checkbox reviews

[anp]

@alexcrichton, #61 (comment) -- this was definitely missed. Need to look at logs.

[anp]

So it looks like this was happening because rfcbot set the reviewed status to true in the database, and then afterwards set it back when it parsed the status comment and the box hadn't been checked. Oops!

Quick fix: don't allow unchecking items to revert a reviewed status after rfcbot knows about it. This might be a problem down the road but will fix things for @michaelwoerister @vadimcn and @withoutboats who have been using the fcp reviewed command instead of the checkboxes.

[bjorn3]

Maybe also check the checkbox when it sees a review.