Scrolling windows in 2.0

[lynch@aristotle.ils.nwu.edu (Richard Lynch)]

I need a window to be able to scroll horizontally from -N1 to N2.
-N1 and N2 are not known until after view-draw-contents is done.
I tried just loading in scrolling-windows and making a subclass
of scroller that specializes scroll-limits (something like that),
but that function doesn't even seem to get called.

PS:  This is for a hierarchy editor that I will be happy to release
if I ever finish it...