ensure ability to ping and stop daemons is not lost over time

On all our Linux hosts one week old files are cleared from /tmp. On Debian lenny the age estimate seems to be based on access time, on Ubuntu precise - on modification time. On lenny pinging the daemon is enough to prevent deletion of daemon's .pid file from /tmp, on precise .pid files disappear after a week. This pull requests incorporate update of the modification time of the .pid file int the ping pocedure.