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

[Eli Zaretskii <eliz@gnu.org>]

> From: Reuben Thomas <rrt@sc3d.org>
> Date: Thu, 6 Sep 2018 20:58:48 +0100
> Cc: 32651@debbugs.gnu.org
> 
>  I don't understand how you conclude that these are not valid use
>  cases.  E.g., I could have a mode turned on that automatically
>  capitalizes words at the beginning of each sentence, in which case
>  typing "and "and" will produce "And and".  And that is just an example
>  based on 5 sec of thought.
> 
> And I don't understand how, just because you can think of an example, that makes the current behaviour a
> good default! I think we'll have to disagree. I would be happy with a preference, of course.

I'm not claiming the current behavior is a good default, I'm saying it
is there for a long time, and thus takes precedence, because we cannot
possibly poll all those users who see that behavior every day and none
of them complained.

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?