Restart pat on existing session

This changes the behaviour of the pat daemon so that it no longer fails
when called from the command line when there is an existing
session. Instead, it silently kills the existing process and starts a
new one. For example:

  $ pat --status
  pat not running
  $ pat
  pat started (13871)
  $ pat
  pat restarted (13984)
  $ pat
  pat started (14071)
pat: Pedantic typo fix