There's at least one more to merge in.
Side-effects:
* Stop reporting None as displayname and avatar_url in some cases
* Joining a room by alias populates guest-ness in join event
* Remove unspec'd PUT version of /join/<room_id_or_alias> which has not
been called on matrix.org according to logs
* Stop recording access_token_id on /join/room_id - currently we don't
record it on /join/room_alias; I can try to thread it through at some
point.