Integrate perlio:

[ 16496]
Portability and doc tweaks to PerlIO/XS stuff.
We are still "papering over the cracks" a bit,
but now it is good stiff card held on with epoxy.

[ 16495]
PerlIO/XS interface routine and doc updates from
lupe@lupe-christoph.de (Lupe Christoph) in mail
Subject: [For Review] Patch for perlio.c and pods
Message-Id: <20020505084315.GA23900@lupe-christoph.de>
Date: Sun, 5 May 2002 10:43:15 +0200
(Minor tweaks to follow.)
p4raw-link: @16496 on //depot/perlio: 22569500a4329ba00826e9a263a1e15c2b24247f
p4raw-link: @16495 on //depot/perlio: 8dcb57838133afcca1063f491fdd55188f1d84ed

p4raw-id: //depot/perl@16497