bug#40725: 27.0.91; Tutorial reports false positive key rebindings

[Eli Zaretskii <eliz@gnu.org>]

> From: "Basil L. Contovounesios" <contovob@tcd.ie>
> Date: Mon, 20 Apr 2020 00:31:25 +0100
> 
> 0. emacs -Q
> 1. M-x winner-mode RET
> 2. C-h t
> 
> The user is then presented with the following:
> 
>  NOTICE: The main purpose of the Emacs tutorial is to teach you
>  the most important standard Emacs commands (key bindings).
>  However, your Emacs has been customized by changing some of
>  these basic editing commands, so it doesn't correspond to the
>  tutorial.  We have inserted colored notices where the altered
>  commands have been introduced. [More]
> 
> Yet no such coloured notices are to be found in TUTORIAL, since
> winner-mode binds only 'C-c <left>' and 'C-c <right>', neither of which
> is mentioned in the tutorial.
> 
> Pushing the "More" button gives the following *Help* buffer contents:
> 
> --8<---------------cut here---------------start------------->8---
> The following key bindings used in the tutorial have been changed
> from the Emacs default:
> 
>    Standard Key   Command                     In Your Emacs   
>    C-c 		  mode-specific-command-prefix M-x mode-specific-command-prefix more info
> 
> It is OK to change key bindings, but changed bindings do not
> correspond to what the tutorial says.
> --8<---------------cut here---------------end--------------->8---
> 
> Pushing the "more info" button in turn gives the following *Help* text:
> 
> --8<---------------cut here---------------start------------->8---
> Your Emacs customizations override the default binding for this key:
> 
> The default Emacs binding for the key C-c is the command
> ‘mode-specific-command-prefix’.  However, your customizations have
> rebound it to the command ‘(keymap (keymap (right . winner-redo) (left
> . winner-undo)) mode-specific-command-prefix)’.
> --8<---------------cut here---------------end--------------->8---
> 
> The following patch fixes this:

Isn't the patch too general?  How do we distinguish the case where
_all_ of the subcommands were rebound, for example?  Also, don't we
have some prefixes that for the purposes of the tutorial must not have
_any_ of its subcommands rebound?

> I don't think this qualifies as urgent enough for inclusion in emacs-27,
> but I think the fix is harmless enough if desired.  WDYT?

The release branch should at this point only accept changes that are
really urgent (and documentation fixes).  This one isn't, IMO.

Thanks.