bug#1149: 23.0.60; C-h m should mention command that toggles mode and its file

[Drew Adams]

> > The description of a (major, or minor, for that matter) mode should
> > also mention the name of the command that turns it on and off.
> 
> It's the same for all minor modes, so that just seems like unnecessary
> verbiage.

How to toggle a minor mode is a frequently posed question.
`C-h m' should speak to it.

It's the same for all minor modes, and it should be stated in
the output of `C-h m'.  It need be said only once for all
minor modes, but it should be said.  It shouldn't take more
than a sentence.

Another frequent question is how to turn OFF a major mode.
It's not obvious that the answer is to turn ON some other
major mode.

And yes, the command that turns ON a given major mode should
be given by `C-h m'.  This too is not obvious, at least for
some major modes.

> > And it should provide a link to the file that defines that
> > command (and the mode).
> 
> I've now added links to the documentation of the mode, which
> provides further links.

Thank you for that.  I won't see the result for a while.
I hope that the rest of this bug gets fixed as well, if
it hasn't been already.