bug#15999: 24.3.50; Redisplay broken with split windows

[Stephen Berman <stephen.berman@gmx.net>]

A recent change -- my guess is this one (I don't have time now to bisect
to confirm this suspicion):

115272: Stefan Monnier 2013-11-28 Refine redisplay optimizations to only
redisplay *some* frames/windows

-- has broken redisplay with split windows.  To reproduce:

0. emacs -Q
1. M-x display-time-mode
3. C-x 2 (or C- x 3)
4. C-x b, so one window displays *scratch* and the other *Messages*.
5. When the displayed time changes, only the current buffer is updated;
   in the other buffer the time display is unchanged, and the scroll bar
   disappears (note my build does not use toolkit scroll bars, I don't
   know if that makes a differences.)  This states of affairs remains
   until the non-updated buffer becomes current.


In GNU Emacs 24.3.50.14 (x86_64-suse-linux-gnu, GTK+ Version 3.10.2)
 of 2013-11-29 on rosalinde
Bzr revision: 115285 schwab@linux-m68k.org-20131129112504-5izsans1kw88maan
Windowing system distributor `The X.Org Foundation', version 11.0.11403901
System Description:	openSUSE 13.1 (Bottle) (x86_64)

Configured using:
 `configure --without-toolkit-scroll-bars CFLAGS=-g3'

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Message

Minor modes in effect:
  diff-auto-refine-mode: t
  gnus-message-citation-mode: t
  mml-mode: t
  shell-dirtrack-mode: t
  show-paren-mode: t
  recentf-mode: t
  display-time-mode: t
  electric-pair-mode: t
  electric-indent-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  temp-buffer-resize-mode: t
  column-number-mode: t
  line-number-mode: t
  auto-fill-function: message-do-auto-fill
  abbrev-mode: t