Fix !ComboBox drop down positioning problem when:   1. the drop down's width has been increased to match the width of the !ComboBox   2. the page has a horizontal scrollbar, and has been scrolled
Fix !ComboBox drop down positioning problem when:
  1. the drop down's width has been increased to match the width of the !ComboBox
  2. the page has a horizontal scrollbar, and has been scrolled

There's still an issue on IE8 in RTL mode though, listed in #11376.

Fixes #11364, refs #10581, #11376.

git-svn-id: 674a2d6b1e32e53f607eb824547723f32280967e@22393 560b804f-0ae3-0310-86f3-f6aa0a117693

redaktor/deliteful