Windows: Support scrolling in long menus or use multipane menus

Long menus such as View->Syntax are a pain to use in Windows. They are not scroll-wheel aware, leaving repeatedly clicking of the "down" arrow as the only way to scroll the list.

Two ideas:

* Hook the mouse scroll wheel when over these menus.

* Break long menus into a series of menu panes stacked horizontally next to each other. This can be seen in some other Windows applications, e.g. XP's Start->Programs menu.