Comment 8 for bug 778256

According to some debug printfs I added to PanelTray.cpp, both GetAbsoluteGeometry() and GetRootGeometry() always return coordinates relative to the top-left corner of a panel.

(And, for extra fun, the systray window is repositioned twice: once for the panel on the left screen, and once for the panel on the right screen. This would cause extra fun if my screens had different widths.)