ComboBox test fails: scrolling problems

[haysmark]

In FF3 (not FF2):

1. In test_ComboBox, move your mouse to the long ComboBox? of dijits.
2. Double-click and press backspace to clear the input.
3. Press down until you reach the end of visible portion of the list.
4. Press down a few more times. Notice that the window has started scrolling a little too, moving the mouse closer to the menu.
5. Press down until the body scrolls so much the mouse is over the ComboBox? menu.

Now that the mouse is over the menu, whenever pressing down would cause the menu to scroll, the body also scrolls and triggers a mouse move event, so the mouse fights with the down arrow key for control of the menu. The result is that it is hard to make progress scrolling through the menu.

The body really shouldn't be scrolling at all.

[Douglas Hays]

[16714] Fixes #8665 !strict. Handle double scrollbars and add testcase.