ignore_sbar is a flag that we set while manually changing the
scrollbar settings, so that when those half-finished changes trigger
GTK event callbacks, we know to ignore them, and wait until we've
finished setting everything up before actually updating the window.
But somehow I had managed to leave the functions that actually _have
the effect_ (at least in GTK1) outside the pair of statements that set
and unset the ignore flag.
The effect was that compiling pterm for GTK1, starting it up, and
issuing a command like 'ls -l' that scrolls off the bottom of the
window would lead to the _top_ half of the ls output being visible,
and the scrollbar at the top of the scrollback rather than the bottom.
c74d1e3c6a