send player counts, local and expected. Based on these the relay
accepts connections, declares the game full and ready for message
forwarding, and decides whether to accept a reconnect.
scheme where cookie is used only to connect, and is replaced for
reconnects by a relay-generated name that's supposed to be unique
across all games on all relays and includes a hostname read in from
config file; relay assign non-servers' hostIDs.
kill crefs via state machine, and protect access to a cref so it can
die without another thread being in it; do timers via timeout to
poll() rather than interrupt (and integrate into state machine);
detect when all players are present and change state so new
connections on that cookie will get a new cref.
