Improve display of long/off-screen popup menus

At least on Win Vista, popup menus with long lists never show a scroll bar or other way (e.g., expansion arrow) to tidy up long or off-screen lists.

Also, there seems to be a general goof where popup menus don't always extend out in the optimum direction. To clarify, near the bottom of the screen, it is best if the popup list extends upward from the menu button. This will eventually happen, but only if your button is VERY close to the edge of the screen, and it doesn't seem to depend on the length of the list that will display. This can lead to menus that run off-screen.