bug#20493: 25.0.50; next-error in change-log-mode can hide its buffer

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@linkov.net>
> Cc: 20493@debbugs.gnu.org,  dgutov@yandex.ru
> Date: Sat, 21 Apr 2018 22:53:05 +0300
> 
> >   . next-error-select-buffer should be documented in the Emacs manual
> >   . the doc string of next-error-select-buffer should be expanded to
> >     explain the effect of selecting a buffer.  The current text is
> >     quite cryptic, IMO: "set it as the last used."  The meaning of
> >     "last used" in this context should be explained.
> >   . next-error-find-buffer-function should perhaps be mentioned in the
> >     Emacs manual and/or the ELisp manual.
> >   . the doc string of next-error-find-buffer-function should describe
> >     the arguments with which it is called, what possible values it can
> >     return, and the meaning of each returned value.
> 
> Done.  I'll try not to forget about updating the documentation and NEWS
> for future changes.

Thanks.

When you describe new commands and variables, please make sure they
are indexed (I added index entries for the ones you documented in this
changeset).