bug#19846: 25.0.50; Problem with auto-fill-mode and C mode

[martin rudalics]

With current trunk/master and emacs -Q evaluate the following form

(add-hook
 'c-mode-hook
 '(lambda ()
    (turn-on-auto-fill)
    (set (make-local-variable 'fill-column) 72)))

and visit ~/src/xterm.c.  Go to the end of that file, move a few lines
backwards so that point is at the beginning of some non-empty line
within the doc-string of `x-frame-normalize-before-maximize' (which is
coded as a C comment).  Now keep the SPC key pressed.  Here Emacs
consumes the entire available CPU and eventually redisplay gets stuck
completely.  This used to work without problems in Emacs 24.3.

In GNU Emacs 25.0.50.1 (i686-pc-mingw32)
 of 2015-02-12 on MACHNO
Repository revision: da726ad0c6177a3442a374a135f40a24945d362c
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --prefix=/c/emacs-git/trunk --enable-checking=yes
 --enable-check-lisp-object-type=yes 'CFLAGS=-O0 -g3''

martin