bug#7440: 23.1; exiting emacs (-nw mode) clears screen scrollback buffer

[ach@google.com (Andy Huang)]

Using emacs -nw within a screen session (w/ altscreen on) clears out
the scrollback buffer upon exit. Repro steps:

- Start GNU screen (w/ the "altscreen on" setting)
- Hit return a few times in the console
- Open emacs in -nw mode
- Exit emacs
- Upon exiting, info above the current line is empty

Note that this doesn't occur when using emacs outside of screen and it
doesn't occur with vi/less or any other editor I've tried. Per a
coworker, this appears to be a regression between 22.2.1 and 23.1.


In GNU Emacs 23.1.1 (x86_64-pc-linux-gnu, GTK+ Version 2.20.0)
 of 2010-03-29 on yellow, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.10706000
configured using `configure  '--build=x86_64-linux-gnu' '--host=x86_64-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib' '--localstatedir=/var/lib' '--infodir=/usr/share/info' '--mandir=/usr/share/man' '--with-pop=yes' '--enable-locallisppath=/etc/emacs23:/etc/emacs:/usr/local/share/emacs/23.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.1/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/23.1/leim' '--with-x=yes' '--with-x-toolkit=gtk' '--with-toolkit-scroll-bars' 'build_alias=x86_64-linux-gnu' 'host_alias=x86_64-linux-gnu' 'CFLAGS=-DDEBIAN -g -O2' 'LDFLAGS=-g' 'CPPFLAGS=''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: C
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: C
  value of $LC_NUMERIC: C
  value of $LC_TIME: C
  value of $LANG: en_US.utf8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default-enable-multibyte-characters: t

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  tool-bar-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  blink-cursor-mode: t
  global-auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<help-echo> <help-echo> <escape> x b u <tab> <backspace> 
<backspace> b u g <backspace> <backspace> <backspace> 
r e p <tab> o <tab> r t <tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list... [3 times]
insert-for-yank: Buffer is read-only: #<buffer *GNU Emacs*>