bug#15917: 24.3.50; manual: mention keys reserved for users

[Drew Adams]

> > >   GNU convention stipulates that key sequences that consist
> > >   of C-c followed by a letter are reserved for users.  Emacs
> > >   Lisp code that follows the convention does not bind these
> > >   keys, so that they are free for personal use.
> >
> > Perhaps "GNU coding convention" would be even clearer than
> > "GNU convention."
> 
> It is wrong to speak about GNU (coding) conventions here, since this
> is not about GNU or coding, this is about key bindings in Emacs, and
> in Emacs alone.

Sure.  If you think that wasn't clear enough then
"GNU Emacs coding convention".  Or "Emacs Lisp
coding convention".  Or "GNU Emacs Lisp coding
convention".

The point is to use the active voice, and to make
clear that this is conventional - a recommendation,
and that code that follows this convention won't
bind these keys.