bug#23179: 25.0.92; Restore `M-,' to continue etags search

[Eli Zaretskii]

> Date: Tue, 2 Apr 2019 07:47:39 -0700 (MST)
> From: pklammer <emacs@pklammer.org>
> 
> I use tags-search (bound to F9 in my .emacs) and then tags-loop-continue M-,
> "all the time".

We should welcome patches to provide implementation of tags-search
based on Xref machinery.  Would you or someone else like to work on
that?

> I found the attitude (3 years ago today) about this breakage very dismissive
> and inconsiderate.

There was a long discussion about that (in addition to the one in this
bug report).

> I would have appreciated it if there were some better breadcrumbs to follow
> to restore familiar operation.

The change was called out in Emacs 25.1's NEWS (as all user-visible
changes are).