Feature ZK-1583: notification arrow position shall align in the center of reference widget
http://tracker.zkoss.org/browse/ZK-1583
Fix bug ZK-1587: Textbox value is wrong when popup close, IE only
http://tracker.zkoss.org/browse/ZK-1587
fine tune
Merge remote-tracking branch 'VincentJian/B60-ZK-1587' into 6.0