bug#20629: 25.0.50; Regression: TAGS broken, can't find anything in C++ files.

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 20629@debbugs.gnu.org
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Sat, 30 May 2015 01:36:56 +0300
> 
> On 05/29/2015 11:35 PM, Eli Zaretskii wrote:
> 
> > xref expects more accurate results, because it shows them all at once,
> > instead of one by one, in some order that assures the users will only
> > ever see the few first ones.  So yes, I'd say the switch to xref puts
> > a different kind of pressure on what etags/ctags does.
> 
> It does exert some pressure, but mostly to ensure that when a user 
> searches for a "symbol" that they see in a buffer, it should have an 
> explicit or an implicit tag match.

The crucial difference is that the number of matches must now be
small, something that required us to remove the method which could
cope with qualified tags when the symbol at point was unqualified.

> Whether qualified tag names are included in the completion, and whether 
> one can search for a qualified tag name reliably, that hasn't changed 
> between find-tag and xref-find-definitions.

True.  But the original arrangement worked well with both with
find-tag and with completions; now that we removed tag-symbol-match-p
and qualified names, completion is less user-friendly.

So I think we should default to having 2 entries for each such tag.