bug#5809: 23.1.94; cross-reference by anchor yields in accurate position

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: juri@jurta.org,  5809@debbugs.gnu.org
> Date: Thu, 01 Apr 2010 18:16:04 -0400
> 
> > Here's another, perhaps better idea: how about if, instead of
> > inserting breadcrumbs as text into the buffer, we put an overlay there
> > with a display property whose value is the breadcrumbs as a string?
> > This way, buffer positions are not affected at all.
> 
> That was my thought as well, but then you can't "click" on breadcrumbs
> with the keyboard any more.

"Clicking" on breadcrumbs with a keyboard is the same as typing "u",
so I don't see this as a loss.  And if we think this _is_ a loss, we
could add a new feature.  Or maybe using the `cursor' property on the
overlay will do the trick even without any new features.