- Force select_for_update order to prevent deadlocks. Many thanks to [jpulec](https://github.com/jpulec) for pointing this out in #29.
- Support passing `of` argument to internal select_for_update. Can be useful in working around "SELECT FOR UPDATE cannot be applied to the nullable side of an outer join". Pull request 27, thanks [osroca](https://github.com/osroca)!