When the extended command menu is big enough to need a scrollbar,
leave more elbow room when forcing its height to fit on screen.
The last entry was frequently obscured by OSX's "docking tray"
desktop decoration and the resize hotspot (bottom right corner of
the menu popup) could be hard to access.
I'm not particularly happy with this code. There really has to be
a better way to accomplish what's needed.
d91b2e5fd7