- Server crashed with 'DIE userdata_unregister called while nonexistent'; fix!

- Store message as UTF8 text, not blob
- Somehow communicate (push? poll?) to room members whether a particular user is currently _active_, not just online.
- A session is marked inactive 2 minutes after the latest activity on that session. Make the number "2" configurable and not a hard-coded constant.
- Use poll(2), not select(2)
- Use single sql query in broadcast.c to get all receiving users, don't perform a JOIN in user code
- Fix OOM dos vector
- Public rooms, and public room join command