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

[Eli Zaretskii]

> Date: Fri, 1 Apr 2016 10:55:46 +0200
> From: Anders Lindgren <andlind@gmail.com>
> 
> I often use "etags" to search in files. The key binding `M-,' used to be 
> bound to `tags-loop-continue', a generic
> command used to continue the last tags operation, like `tags-search' and 
> `tags-query-replace'.
> 
> In Emacs 25.0.92, `M-,' is bound to `xref-pop-marker-stack', whereas 
> `tags-loop-continue' is unbound.
> 
> Clearly, this breaks things for existing etags users and brings very little 
> in return.

Please describe the use case where you needed to invoke
tags-loop-continue.  I think we made an effort to eliminate these use
cases (by providing alternatives that are built on top of xref), but
maybe some slipped through the cracks.

> (I expect `xref-pop-marker-stack' to be used relatively seldom.)

Like Dmitry, I use it all the time.  You really cannot avoid using it,
since, unlike find-tag, xref-find-definitions doesn't push a mark
storing the place where you invoked "M-.", so the only reasonable way
of getting back is with "M-,".