screen broken in 1.4.0

[joerg@xxxxxxxxxxxxxxxxx]

Another last minute bug. Something in the tty / signal related changes
between 1.3.7 and 1.4.0 made screen pretty much unusable. It doesn't
correctly update the display anymore when a scroll-down would occur.
E.g. in irssi, the last three lines are only partly updated and the text
above is not scrolled up.

Joerg