Comment 329 for bug 1084

Since em is the equivalent of font-size, while ch is the equivalent of the width of the 0 character, what would that buy us (other than the all-important CHee-factor, of course)? A shorter pane for people using a font that's narrower than average?

And since I don't think we should ignore the problem addressed by Kurosawa-san's patch, that if you trigger All Headers while you have the height of the message pane smaller than the max-height we give to expandedHeaderView, it will still spill over the statusbar, we only need to argue about appropriate units if someone has an idea for setting minHeight on the message pane in a way other than through .minHeight.