bug#20240: 25.0.50; CC Mode broken fontification and commenting

[Mark Oteiza]

>From emacs -Q:

1. C-x C-f foo.c RET
2. Insert: { RET }
3. Select the first line and M-;

Only `/* ` is inserted at the beginning of the buffer, which is wrong.

4. Undo: C-/

The braces remain fontified as comments.

In GNU Emacs 25.0.50.1 (x86_64-unknown-linux-gnu, X toolkit, Xaw scroll bars)
 of 2015-03-31 on logos
Repository revision: 8d1d8fc474bd9ed22cbe8b80125c8ce89dc62b57
Configured using:
 `configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --without-gconf --with-x-toolkit=lucid
 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong
 --param=ssp-buffer-size=4' CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB

Important settings:
  value of $LC_COLLATE: C
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix