GUIWindowPVR: don't spawn dedicated thread just to invalidate channel items every 5 seconds. Instead run CStopWatch when activating channel window, check if 5 seconds elapsed and then inavlidate window and reset watch.
Merge pull request #2628 from pieh/kill_pvrwindow_thread

GUIWindowPVR: don't spawn dedicated thread just to invalidate channel items every 5 seconds