bug#24521: 25.1; background color difference in dark themes on blank lines and first column

[Tijs Mallaerts <tijs.mallaerts@gmail.com>]

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To reproduce:
- keep the default theme (of emacs -q) or switch to another theme with a
dark background (f.ex. deeper-blue)
- switch to the scratch buffer
- zoom in to +3
- hit Return a few times

A slight difference of the background color is visible between the lines on
which Return was hit and the blank lines. The first column has a different
background color as well.

In GNU Emacs 25.1.2 (x86_64-unknown-linux-gnu, GTK+ Version 3.18.9)
 of 2016-09-17 built on kubuntu
Windowing system distributor 'The X.Org Foundation', version 11.0.11803000
System Description:    Ubuntu 16.04.1 LTS

Configured using:
 'configure --with-xwidgets'

Configured features:
XPM JPEG TIFF GIF PNG SOUND DBUS GSETTINGS NOTIFY LIBXML2 FREETYPE XFT
ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 XWIDGETS

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

Major mode: Lisp Interaction

Minor modes in effect:
  text-scale-mode: t
  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.
Use +,-,0 for further adjustment [4 times]
C-x C-: is undefined
C-: is undefined [2 times]
Use +,-,0 for further adjustment [3 times]

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message dired format-spec rfc822 mml
mml-sec password-cache epg epg-config gnus-util mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util help-fns help-mode easymenu
cl-loaddefs pcase cl-lib mail-prsvr mail-utils face-remap time-date
mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel 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 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 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 xwidget-internal move-toolbar
gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 89233 7884)
 (symbols 48 19692 0)
 (miscs 40 100 121)
 (strings 32 14434 3546)
 (string-bytes 1 417157)
 (vectors 16 11807)
 (vector-slots 8 431663 4621)
 (floats 8 167 196)
 (intervals 56 252 0)
 (buffers 976 19)
 (heap 1024 44757 1092))

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