Properly daemonize the mail_room process

The old invocation only worked by accident because we have a '&' somewhere in the init script for expediency. When ran from a terminal, the mail_room daemon process ended up in the session of the terminal. This commit adds a small wrapper that tries to do the textbook daemonization steps (double fork, setsid etc.) while also taking care that the pidfile is written before the 'start' process exits.