bug#22692: docstring for xref-find-definitions

[Drew Adams]

> >> It's a breaking one, but it primarily affects xref (aside from the
> >> "obsolete" etags commands). And by doing it now, we can avoid similar
> >> breakage in the next Emacs release.
> >
> > Exactly my thoughts.
> > So I think you should push your change, unless Juri objects.
> 
> I'm fine with using bounds-of-thing-at-point if you think it's OK
> to require thingatpt in core packages such as isearch.

Wrt `bounds-of-thing-at-point', please consider fixing bug #9300.
The fix was provided, and it is trivial.

See also `bounds-of-thing-at-point' bug #8667.