* client.cpp (main): Get t_old early since it is used on error exits.
* server.py (Client.checker): New attribute. (Client.check_action, Client.start_checker, Client.stop_checker, Client.fileno, Client.next_stop, Client.still_valid, Client.it_is_time_to_check): New methods. (Client.handle_request): Alias to "check_action". (main): Stop all started checkers on exit. Exit cleanly on keyboard interrupt.