bug#17321: 24.3.50; Fill paragraph fails with period in fill-column

[Geoff Shannon]

When the final character on a line is a period, auto filling both with
do-auto-fill and with fill-paragraph incorrectly moves the entire word
preceding the period to the next line.  This is not the case when it is
a letter in the fill-column.

To reproduce, `emacs -Q` Then load up this text in a buffer, and turn
auto-fill-mode on, and assuming that fill-column is set to 70.

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eius.

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusm

Both lines are the same except for the final character.  If we type a
space at the end of both lines, the one word with a trailing period is
(incorrectly) moved to the next line, while the other does nothing.

This behaviour doesn't seem to be tied to the value of fill-column (I
tried it with a few 5 and 70).

I've attached a dribble file, starting from 'emacs -Q' that illustrates the
filling issues I'm talking about.

Also, it appears that setting sentence-end-double-space changes the behaviour to what I would expect.  However, in terms of the aesthetic result of the fill, I think the current behaviour is still incorrect.

In GNU Emacs 24.3.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.6.4)
 of 2014-01-01 on minty-dark-tower
Bzr revision: 115828 eggert@cs.ucla.edu-20140101231359-pzcy6lepssiaboye
Windowing system distributor `The X.Org Foundation', version 11.0.11303000
System Description:    Linux Mint 15 Olivia

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Text

Minor modes in effect:
  tooltip-mode: t
  electric-indent-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
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
C-x b <return> C-e C-a C-x b <return> C-SPC C-e M-w
M-x r e p o r t <tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
easymenu mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util help-fns mail-prsvr mail-utils time-date tooltip electric
uniquify ediff-hook vc-hooks lisp-float-type mwheel x-win x-dnd tool-bar
dnd fontset image regexp-opt fringe tabulated-list newcomment lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core frame cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese case-table epa-hook jka-cmpr-hook help simple abbrev
minibuffer nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote make-network-process
dbusbind gfilenotify dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty emacs)

filldribble
Description: Binary data