Shut down if no users connect during startup

[nchlswhttkr]

Right now, the server's script waits for someone to connect to consider itself "started". This is straightforward, but if nobody ever connects then the instance will never shut down.

until has_active_connections; do sleep 5; done

I've already forgotten to check for running instances before. It would be good to add a timeout (say 15 minutes) so the server shuts down if nobody joins after it is started.