This patch adds support for sending the USR1 and USR2 signals to a
supervised process.

It modifies the "svc" program to accept the flag "-1" to send a SIGUSR1,
and the flag "-2" to send a SIGUSR2.

It also modifies the "supervise" program to watch for the commands "1"
or "2", and send the supervised process a SIGUSR1 or SIGUSR2 signal,
respecively.