refix for B70-ZK-2366 and B70-ZK-2368
Bug ZK-2400: In IE8, clicking the "up/down" arrow of timebox triggers an onChange event every second time
Bug ZK-2402: In IE8, clicking the "up/down" arrow of timebox does not always trigger an onChange event
Merge pull request #111 from hanhsu/refix-B70-ZK-2366

refix for B70-ZK-2366 and B70-ZK-2368