bug#15716: 24.3.50; redisplay bug for display-table update

[Drew Adams <drew.adams@oracle.com>]

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This seems to be a regression; I have never seen it before.

See attached screenshots, from the same session.  The bad one (NG) was
taken after `C-l', which should have taken care of any redisplay
problem.  The good one (OK) was taken after then iconifying (thumbifying,
actually) and then restoring the frame - that took care of the display
problem.

The part of the displayed buffer that got messed up is the result of
modifying the display table for character ^L - what looks like a sunken
line of text "Section (Printable Page)" is in fact just a ^L character.
The code that does this is here:
http://www.emacswiki.org/emacs-en/download/pp-c-l.el.

This is the part of the code that updates the display table:

(lambda (window)
  (let ((display-table  (or (window-display-table window)
                            (make-display-table))))
    (aset display-table ?\014 (and pretty-control-l-mode
                                   (pp^L-^L-display-table-entry window)))
    (set-window-display-table window display-table)))

BTW/FWIW - I think I have also noticed, with this build (perhaps other
recent builds too?), the need to hit `C-l' more often.  Until now I have
probably used `C-l' only a few times over the last decade or so - hasn't
been needed.  (In the old days it was needed much more often.)

HTH.



In GNU Emacs 24.3.50.1 (i686-pc-mingw32)
 of 2013-10-19 on LEG570
Bzr revision: 114715 rgm@gnu.org-20131019023520-s8mwtib7xcx9e05w
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --enable-checking 'CFLAGS=-O0 -g3' CPPFLAGS=-DGLYPH_DEBUG=1'

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