make the use of the 5-argument @xref command consistent

make the use of the 5-argument @xref command consistent

A few of the @xref references to external manuals in the documentation
are using an old 4-argument form that produces an undefined reference
in the printed manual.  The following patch makes them consistent with
the 5-argument @xrefs used elsewhere in the manual.

--
Brian Gough

Network Theory Ltd,
Publishing Free Software Manuals --- http://www.network-theory.co.uk/

>From 6ca0417830dc5a98699a15808591dc1f2a90dfac Mon Sep 17 00:00:00 2001
From: Brian Gough <bjg@gnu.org>
Date: Mon, 14 Dec 2009 21:34:59 +0000
Subject: [PATCH] make the use of the 5-argument @xref command consistent
 when referring to other manuals.