bug#19468: 25.0.50; UI inconveniences with M-.

[Drew Adams <drew.adams@oracle.com>]

> > - When I try to jump to a symbol, and there isn't one with that
> >   name, I want to see the message "no definitions found", not a
> >   "Visit tags table" prompt.
> 
> I tend to agree.

IIUC, that seems a bit ironic.

You took the opposite point of view when I said the same thing
about `completion-styles' that you seem to be saying here.

I made just that argument: let users know when a given completion
method finds no matches, and let them choose whether to go on to
trying another method.

This seems similar - the difference being that instead of
different ways of matching completion candidates you are dealing
with different "backends" their candidate sets.

Giving users feedback such as "No definitions found" and "No
completions", instead of blindly going on to look for other
hits using other means, is helpful and gives them more control.

At the very least it should be an option: let them decide
whether to go on automatically to other attempts.

Which is also the argument I made wrt `completion-styles':
let users choose which styles should chain automatically to
which others, by grouping them.  No group(s) means no automatic
chaining.