Popup menu click-hover-click-again doesn't work near edge of viewport

[justvanrossum]

We have two menu select behaviors:

1. click-drag and release on disired menu item
2. click, hover (or type arrow key) to the desired item, then click or type enter

When the menu panel gets moved because it would otherwise be clipped by the viewport, the second method no longer works.

This does work correctly for the context menu, as it succesfully seems to avoid the pointer location.

I think the problem is with the mouse-up logic: it currently selects if mouse-up is on a selectable menu item. It should probably only do that if the pointer at least moved some minimal distance.