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

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@users.sourceforge.net>
> Cc: 24051@debbugs.gnu.org,  drew.adams@oracle.com,  phillip.lord@russet.org.uk
> Date: Mon, 29 Jan 2018 19:38:38 -0500
> 
> Hmm, it's a bit of an awkward fit, but yes, worth a mention (and actual
> cross-references are only to nodes, not a single function entry, so "the
> previous section" is already all the cross-reference needed, right?).

"Previous section" is harder to follow in the on-line manual,
especially if some day that section will acquire subsections.

> Okay, here's the full patch, please double check my texinfo.

LGTM, with the minor comments already voiced.