* on "QUIT" command. In replay mode, exits with 0 on each non-"QUIT" command.
* Writes a "PONG" line to server output file on "PING" command. In play mode,
* processes further incomming commands via obey_msg(). Compares the first line
* on "QUIT" command. In replay mode, exits with 0 on each non-"QUIT" command.
* Writes a "PONG" line to server output file on "PING" command. In play mode,
* processes further incomming commands via obey_msg(). Compares the first line