* sysdep.c: added new event hook type EVT_TIMER. Timer event hooks are called

* sysdep.c: added new event hook type EVT_TIMER.  Timer event hooks are called
  once per minute by any worker thread.
* msgbase.c: removed dependence on nested functions in CtdlOutputMsg() by
  replacing them with an API call CtdlRedirectOutput() in sysdep.c, which
  can temporarily redirect a session's output to an arbitrary file or socket.
* serv_smtp.c: implemented the purging of messages in the queue for which all
  deliveries have been completed.
* serv_smtp.c: removed temporary 'QQQQ' server command and replaced it with
  a timer event hook that runs the queue once per minute (this needs to be
  made more robust)