Another proof that 640KB won't be enough for everybody.

This should enable reading upper parts of window even while the output
is still being produced (tail -f).

IOW, the auto-scroll is disabled after scrolling back manually using
S-PageUp or S-PageDown, and re-enabled on another keypress such as
typing when a prompt is expected at the bottom.

Not particularly bright idea.

With transition to tiled window managers, tabbed makes less sense.