Make the idle timeout independent of scheduler runs

As the scheduler runs every other minute when the EIT scanner is
enabled you end up with never being idle, thus breaking shutdown
when idle.

As discussed on IRC at
http://irc.mythtv.org/ircLog/channel/4/2013-03-14:18:52:00

Refs: #11399

mythtv/programs/mythbackend/scheduler.cpp

@@ -1944,7 +1944,8 @@ void Scheduler::run(void)
         {
             MythEvent me("SCHEDULE_CHANGE");
             gCoreContext->dispatch(me);
-            idleSince = QDateTime();
+// a scheduler run has nothing to do with the idle shutdown
+//            idleSince = QDateTime();
         }
 
         // if idletimeout is 0, the user disabled the auto-shutdown feature