bug#33320: 27.0.50; `describe-key' fails to display help for C-mouse-3

[Eli Zaretskii]

> From: Richard Stallman <rms@gnu.org>
> Cc: nljlistbox2@gmail.com, 33320@debbugs.gnu.org
> Date: Fri, 09 Nov 2018 18:02:11 -0500
> 
>   > I don't think we can do that with all toolkits, because once Emacs
>   > pops up the menu, the toolkit has control.
> 
> Are any of the supported display methods not worth supporting any more?
> In principle, we could drop any that users don't care about any more.

I'm not aware of any we want to drop, and the question was about GTK,
which we definitely don't want to drop.