Popup position not properly fixed in listbox

Reproduce:
Use test.zul and TestVM.java in reproduce.zip attached, there are two issues:
1. Scroll browser window is very slow.
2. Open a Datebox or Combobox, the position of popup is out of sync after scroll Listbox.

Cause:
1. Scroll browser window triggered onScroll of Datebox/Combobox, and applys the fix to "Each" Datebox/Combobox even their popup is not opened.
2. Scroll Listbox does not trigger onScroll of Datebox/Combobox so no fix is applied.

Workaround:
Override onScroll of Datebox/Combobox (in this case), only apply the fix to a Datebox/Combobox which has an opened popup,
also override _doScroll of Listbox to fire onScroll event to its children.
Please refer to test.zul in workaround.zip attached.