bug#25482: 26.0.50; Allow setting `query-replace-from-to-separator` to nil

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Cc: Eli Zaretskii <eliz@gnu.org>,  25482-done@debbugs.gnu.org
> Date: Mon, 13 Feb 2017 02:37:56 +0200
> 
> >> So that design decision and the resulting code we have now had some
> >> justification, and any replacement will have to support the same
> >> features, which I think a simple string will not do.
> >
> > Ok, thanks for explanation, perhaps you can close this bug.
> 
> Thanks, Thierry, I installed your second patch (from 20 Jan)
> with some modifications.

Thanks, but please also update NEWS and the Emacs manual with the
information about the new nil value of the separator.  (Maybe it's a
good idea to describe in the ELisp manual the structure of
query-replace-history elements?)