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

[Eli Zaretskii <eliz@gnu.org>]

> From: Thierry Volpiatto <thierry.volpiatto@gmail.com>
> Cc: 25482@debbugs.gnu.org
> Date: Sat, 28 Jan 2017 07:50:19 +0100
> 
> Just to not leave this unfinished, here the last patch I did which
> simplify code.
> 
> - defcustom is simple (string or nil).
> - No need to reevaluate defcustom at every time.
> - setq is usable.
> - splitting is now simple with all the text property dance removed.
> - plain string is added to history instead of a crap string.

Thanks, but I don't understand why you want to get rid of the display
property.  (I also object to calling the result of that "crap".)  I'd
rather we left the display property and its supporting code intact,
and only moved the char-displayable-p call to the place where the
string is used instead of having it in the defcustom, thus allowing
customizations with setq.  That should solve the real problems with
the current code, leaving the style-related issues alone.  I realize
that you don't like that style, but I think we should respect style
preferences of others and not change their code just because we would
have written it differently.