Minimal upgrade docs for 2.3

[Richard Michael Todd]

In message <yl3dv9p13x.fsf at windlord.stanford.edu>you write:
>I've added this section to the beginning of NEWS in the current tree;
>please let me know what else should be included.  The exact command lines
>to rebuild the history and overview files would also be good to include.

[...]
>    The history file format changed between 2.2 and 2.3, as did the
>    overview format.  Regardless of whether you were using the storage API
>    or traditional spool under 2.2, you'll need to rebuild your overview
>    and history files.  The program to use to rebuild the history file is
>    makedbz, not makehistory.  makehistory is used to rebuild the overview
>    database.

Well, not precisely.  Makedbz rebuilds the history *database* files (the
.dir/.pag or .dir/.index files).  The history file itself (the one without
any suffix) is made by makehistory; makehistory can make either the history
file, the overview data, or both.

As for sample command usage, here's the script I run to rebuild
history and overview. It's a bit more elaborate than you probably need
(it tries to preserve the old "expired" msgids from history in the new
file), but should give an idea.  For general use, you'd probably want
to avoid some of the hardcoded paths, like my particular choice of
TMPDIR.  

#!/bin/sh
TMPDIR=/var/spool/news/over.view; export TMPDIR
cd /var/netnews/lib
if time makehistory -b -f history.n -O -T$TMPDIR -l 600000 ; then
   :
else
   echo Error creating history file!
   exit 1
fi
# The following line can be used to retain expired history
# It is not necessary for the history file to be sorted.
awk 'NF==2 { print; }' <history >>history.n
# View history file for mistakes.
if makedbz -s `wc -l <history.n` -f history.n; then
   wc -l history history.n
   mv history.n history
   mv history.n.dir history.dir
   mv history.n.pag history.pag
fi