func (w *Watcher) Start() <-chan *Notification {
	if w.notify_chan != nil {
		return w.notify_chan
	}
	if w.auto_watch {
		w.add_chan = make(chan *watchItem, NotificationBufLen)
		go w.watchItemListener()
	}
	w.notify_chan = make(chan *Notification, NotificationBufLen)
	go w.watch(w.notify_chan)
	return w.notify_chan
}
func (w *Watcher) Start() <-chan *Notification {
	if w.notify_chan != nil {
		return w.notify_chan
	}
	if w.auto_watch {
		w.add_chan = make(chan *watchItem, NotificationBufLen)
		go w.watchItemListener()
	}
	w.notify_chan = make(chan *Notification, NotificationBufLen)
	go w.watch(w.notify_chan)
	return w.notify_chan
}
// Start begins watching the files, sending notifications when files change.
// It returns a channel that notifications are sent on.