bug#28402: 25.2; shr.el uses shr-tag-img despite set shr-external-rendering-functions

[Eli Zaretskii]

> Date: Sun, 24 Sep 2017 15:10:50 +0200
> From: Vasilij Schneidermann <v.schneidermann@gmail.com>
> Cc: 28402@debbugs.gnu.org, larsi@gnus.org
> 
> > Fair enough.  Fortunately, it sounds like Lars have just agreed to
> > that.
> 
> Alright, I finally got to creating a patch for this.

Thanks, this LGTM.  Lars, any comments?

If no objections are voiced in a few days, I will push to the emacs-26
branch.