bug#24051: 24.5; doc of `external-debugging-output'

[Eli Zaretskii <eliz@gnu.org>]

> From: Noam Postavsky <npostavs@users.sourceforge.net>
> Date: Sun, 28 Jan 2018 18:22:41 -0500
> Cc: 24051@debbugs.gnu.org
> 
> I don't think it fits under "Output Functions" though, as it says:
> 
>     This section describes the Lisp functions for printing Lisp
>     objects--converting objects into their printed representation.
> 
> It's rather an example of an output stream, so it should go in the
> previous section:

But you can also mention it there, with a cross-reference.

> --- a/doc/lispref/streams.texi
> +++ b/doc/lispref/streams.texi
> @@ -530,6 +530,12 @@ Output Streams
>  Calling @code{concat} converts the list to a string so you can see its
>  contents more clearly.
>  
> +@findex stderr

stderr is not a function, so @findex is not appropriate for it.  I'd
rather suggest this:

  @cindex @code{stderr} stream, use for debugging

> +@defun external-debugging-output character
> +This function can be useful as an output stream when debugging.  It
> +writes @var{character} to the standard error stream.
> +@end defun

Thanks, this is good for the release branch.