In Review Board 1.7.x, it was possible to enter an ID in the search

field and, if search was enabled for that installation, go directly to

the review request page.
The search rewrite in 2.0 lost this ability. This change adds it back

through the same mechanism.
We probably want to support this functionality directly in the quick

search widget in the future, so that it would work without having to

have full-on search enabled. In the meantime, however, this at least

fixes this particular regression.
It's also worth noting that in 1.7.x, this was broken with Local Sites,

as it tried to use database IDs and not display IDs. This is fixed

properly for 2.0.

Enabled search and typed an ID. Got redirected to the correct review

request.