bug#13751: 24.3.50; regression: font-lock broken since 2013-02-17

[Drew Adams]

1. A user reported that Dired+ highlighting is completely broken now.  I
can confirm that this is so in this build from 2013-02-17, and that it
is not broken in a build from 2013-02-15.
 
If we need to dig further into this we can do so, but this regression
might be related to whatever causes the font-locking regression
described next, #2, and that is trivial to repro.
 
2. Font-locking of Emacs-Lisp files is broken too:
 
emacs -Q

(add-hook 'emacs-lisp-mode-hook 'turn-on-font-lock)
 
Then visit a buffer in Emacs-Lisp mode - no highlighting.
 
A call to `turn-on-font-lock' should never turn off highlighting.  If
already turned on, it should be a no-op.  This has always worked
previously, in Emacs versions going back at least to 20 and probably
(IIRC) to 18.
 
I looked for diffs between 2013-02-15 and -17 for font-lock.el and
font-lock-core.el, but I didn't see anything that stood out.
 
In GNU Emacs 24.3.50.1 (i386-mingw-nt5.1.2600)
 of 2013-02-17 on VBOX-W7
Bzr revision: 111822 rgm@gnu.org-20130217190146-mm9bh3227ev56bus
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.7) --no-opt --enable-checking --cflags
 -IC:/emacs/libs/libXpm-3.5.10/include -IC:/emacs/libs/libXpm-3.5.10/src
 -IC:/emacs/libs/libpng-dev_1.4.3-1_win32/include
 -IC:/emacs/libs/zlib-dev_1.2.5-2_win32/include
 -IC:/emacs/libs/giflib-4.1.4-1-lib/include
 -IC:/emacs/libs/jpeg-6b-4-lib/include
 -IC:/emacs/libs/tiff-3.8.2-1-lib/include
 -IC:/emacs/libs/libxml2-2.7.8-w32-bin/include/libxml2
 -IC:/emacs/libs/gnutls-3.1.8-w32/include
 -IC:/emacs/libs/libiconv-1.14-2-mingw32-dev/include'