This introduces a new front-end function, do_scroll(), which is expected to
scroll a part of the physical display and cause repaint events for any
areas that couldn't be scrolled (e.g. because they were hidden).
scroll_display() is a wrapper around this which also updates disptext to
match.
Currently, scroll_display is only used in response to user scrollback requests
(via term_scroll()), but extending scroll() to use it as well should be
easy.
All of this is conditional on the front end's defining OPTIMISE_SCROLL, since
only the Mac front end currently implements do_scroll().
[originally from svn r2242]
This doesn't include any mkfiles.pl glue, and is missing one or two other
fixes. The terminal emulator is kind of working, though, as, I believe, is
the store module. Everything else is yet to be done.
[originally from svn r2226]
