bug#23086: 25.1.50; Emacs ignores Unicode line and paragraph separator characters

[Philipp Stephani <p.stephani2@gmail.com>]

Type some characters
C-x 8 RET LINE SEPARATOR (or PARAGRAPH SEPARATOR)
Type some more characters
M-q

Expected behavior: Emacs treats these characters as line and paragraph
separators: they are displayed as line breaks, M-q doesn't remove them,
and forward-paragraph etc. treat the paragraph separator as paragraph
end.

Actual behavior: These characters are displayed as one-pixel horizontal
whitespace and otherwise ignore.

Also discussed in
https://lists.gnu.org/archive/html/emacs-devel/2015-08/msg01043.html.
https://www.emacswiki.org/emacs/unicode-whitespace.el supposedly adds
support for these characters, but I think proper treatment of Unicode
separators should be part of Emacs.



In GNU Emacs 25.1.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.10.8)
Repository revision: 780a605e1d2de4b975e6f1f29b491c9af419dcff
Windowing system distributor 'The X.Org Foundation', version 11.0.11501000
System Description:	Ubuntu 14.04 LTS

Configured using:
 'configure --with-modules --disable-build-details 'CFLAGS=-g -O0''

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND GPM DBUS GCONF GSETTINGS NOTIFY ACL
LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 MODULES

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
  global-eldoc-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 messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Quit
Fill column set to 10 (was 70)
Quit
Making completion list...

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message dired dired-loaddefs format-spec
rfc822 mml easymenu mml-sec password-cache epa derived epg epg-config
gnus-util rmail rmail-loaddefs mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils iso-transl time-date mule-util
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel term/x-win x-win term/common-win x-dnd tool-bar dnd fontset image
regexp-opt fringe tabulated-list newcomment elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core term/tty-colors frame
cl-generic cham georgian utf-8-lang misc-lang vietnamese tibetan thai
tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek romanian
slovak czech european ethiopic indian cyrillic chinese charscript
case-table epa-hook jka-cmpr-hook help simple abbrev obarray minibuffer
cl-preloaded 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 dbusbind inotify
dynamic-setting system-font-setting font-render-setting move-toolbar gtk
x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 174467 8982)
 (symbols 48 30106 0)
 (miscs 40 468 148)
 (strings 32 66519 6641)
 (string-bytes 1 1505951)
 (vectors 16 13333)
 (vector-slots 8 488346 23035)
 (floats 8 167 91)
 (intervals 56 233 2)
 (buffers 976 13)
 (heap 1024 43667 1138))

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