Use normal double quotes in TeX / LaTeX comments

Use normal double quotes in TeX / LaTeX comments

* lisp/textmodes/tex-mode.el (tex-insert-quote): When in a comment,
  default to inserting a normal double quote (") instead of TeX-style
  open (``) or close ('') quote marks.

* etc/NEWS (TeX mode): Note the change.

* test/lisp/electric-tests.el (autowrapping-7): Adjust accordingly.

See this thread for discussion:

  https://lists.gnu.org/archive/html/emacs-devel/2016-08/msg00611.html
  From: Karl Fogel <kfogel {_AT_} red-bean.com>
  To: Emacs Development <emacs-devel {_AT_} gnu.org>
  Subject: [PATCH] Have LaTeX mode use normal double quotes in comments.
  Date: Mon, 29 Aug 2016 14:44:12 -0500
  Message-ID: <87twe3icmr.fsf@red-bean.com>