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

[Eli Zaretskii]

> Cc: 23179@debbugs.gnu.org, andlind@gmail.com
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Tue, 5 Apr 2016 20:40:03 +0300
> 
> On 04/05/2016 07:18 PM, Eli Zaretskii wrote:
> 
> > The defcustom can control also which function(s) are called.  Asking
> > users to customize options whose values are functions is something I
> > think we should avoid as much as possible.
> 
> Why? Just describe each option properly. The user will pick between 
> descriptions, not between functions.

Some users use "M-x set-variable", or some Lisp in their .emacs.