window list menu does not scroll

With DockbarX 0.39.7 on Ubuntu 9.10, if you have too many windows open with a single application, the window list menu will exceed the available (vertical, in my case) screen space, and make some of the windows inaccessible.

There are two aspects to this bug:
1. The DockbarX window list is less compact than the equivalent GNOME window list, so the overflow point is reached with fewer windows. Making the list more compact would be desirable.
2. The window list should support some form of scrolling, as does the GNOME window list.

This bug is slightly related to the "group applications when space is limited" blueprint[1] in that both deal with the issue of how you keep UI elements in a consistent location while accommodating limited screen real estate. One option to avoid scrolling might be to use multiple columns.

(Similarly, for the above blueprint, when the dock capacity is exceeded, it could expand to use multiple rows/columns when the mouse is hovering over the doc. Similar to an auto-hide taskbar. That may be challenging to implement, given that menus pop-up on mouse over, and they will obscure the second row/column of group buttons. The user would need to boost the menu delay to make it usable.)

1. https://blueprints.launchpad.net/dockbar/+spec/dockbarx-group-groups/