supervise-daemon: add a --respawn-limit option

Allow limiting the number of times supervise-daemon will attempt to respawn a
daemon once it has died to prevent infinite respawning. Also, set a
reasonable default limit (10 times in a 5 second period).

This is for issue #126.

sh/supervise-daemon.sh

@@ -25,6 +25,7 @@ supervise_start()
 	eval supervise-daemon --start \
 		${chroot:+--chroot} $chroot \
 		${pidfile:+--pidfile} $pidfile \
+		${respawn_limit:+--respawn-limit} $respawn_limit \
 		${command_user+--user} $command_user \
 		$supervise_daemon_args \
 		$command \