bug#16932: 24.3; Fringe does not get correctly updated under very specific circumstances

[David Engster]

I noticed that sometimes icons in the fringe from previous buffers
remained visible when I switched buffers. It was quite difficult to
reproduce, but I finally noticed that it always happens when you switch
to(!) a buffer where

 - point is on a tabulator
 - there's an overlay on that tabulator until the end of the line
 - that overlay has a face property with the fringe's background color

Here's a recipe through which I can reliably reproduce this issue on
GNU/Linux with Emacs from today's trunk:

* Create a file, for instance "test.el", with the following contents:

  (setq-default indicate-buffer-boundaries 'left)

  (defface someface
    `((t (:background ,(face-background 'fringe))))
    "face with same background as fringe")

  (goto-char (point-min))
  (insert "\t\n")
  (setq ov (make-overlay (point-min)
                         (progn (goto-char (point-min)) (point-at-eol))))
  (overlay-put ov 'face 'someface)
  (switch-to-buffer (get-buffer-create "test"))
  (insert "\n\n\n\n")
  (redisplay t)
  (switch-to-buffer "*scratch*")

* Start emacs with

  emacs -Q -l test.el

* In the left fringe, you should see boundary indicators for the current
  scratch buffer as well as for the previously visible buffer 'test'.

-David