bug#32651: flyspell marks doublons when not the same case

[Eli Zaretskii]

> From: Reuben Thomas <rrt@sc3d.org>
> Date: Sun, 9 Sep 2018 20:45:51 +0100
> Cc: 32651@debbugs.gnu.org
> 
>  This is why I suggested a new customizable option: that way, you and
>  anyone else who wants Flyspell to behave differently can have that,
>  and if we learn this is the preferred behavior (by getting requests to
>  set that as default), we can make it the default at some future point.
>  IOW, what I suggested is a path towards potentially changing the
>  default, but gradually and without backward incompatibilities.  OK?
> 
>  OK!
> 
> Attached, a patch. If the code's OK, I can write a NEWS entry (anything 
> else?).

NEWS should be enough, I think.  Also...

> +(defcustom flyspell-case-fold-duplications t
> +  "Non-nil means Flyspell matches duplicate words case-insensitively."
> +  :group 'flyspell
> +  :type 'boolean)

This defcustom should have the :version tag.

Thanks.