Comment 3 for bug 1172936

At Galen's recommendation, I've added a backstop to avoid the possibility of an infinite while-loop, were we to get into a situation where either timing conspires to keep a looping process behind other attempts at a search, or our automatic cache expiration fails us. Because the stub timeout is 1/3 of $cache_timeout, the backstop of a full $cache_timeout span seems reasonable. Same bat-repo, same bat-branch.