hours miscalculated for shifts ending at midnight

Definitely there's a better solution, though I fixed it as below in function shift_scheduler_old_shifts_results:

		if ($ett < $stt){
			$total_duty +=$ett + 24 * 3600 - $stt;
		}else{
			$total_duty += $ett - $stt;
		}

Please do some test on the latest build here:
http://drupalcode.org/sandbox/mcstrother/1075572.git/commit/a2005e9

issue closed.