bug#11680: flyspell should use mouse-3 instead of mouse-2

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Kangas <stefan@marxist.se>
> Cc: 11680@debbugs.gnu.org,  l26wang@gmail.com
> Date: Thu, 16 Jan 2020 02:50:19 +0100
> 
> > Fine with me, but that button is already bound to
> > mouse-save-then-kill.  I never use it, but what will those who do say?
> 
> Since this key binding is only in flyspell-mouse-map, it will only be
> rebound when the mouse pointer is over a misspelled word.  Note that
> mouse-2 is normally bound to mouse-yank-primary.

I don't see how this resolves the backward-compatibility issue, sorry.

> I therefore don't think it will be a big problem in practice.  On the
> contrary, I believe that having the context menu on the right mouse
> button will feel more natural and be more discoverable to users.

Once again, we are not talking about adding a new feature from
scratch, we are talking about changing a very old behavior.  So
whether it's more natural or not is of secondary importance for this
decision.

I'm okay with making this conditional on some user option, but I
object to an unconditional change.

> I have attached an updated patch below.  If there are no objections to
> it, would this change be safe for the release branch, or should it go
> to master?

In any case, we don't add new features on the release branch, we only
fix bugs there.

Thanks.