tags LINUXDOC_2_DOCBOOK_START and LINUXDOC_2_DOCBOOK from doc/handbook/.

Note that the LINUXDOC_2_DOCBOOK tag is not necessarily at the HEAD of
the file. So some files won't show changes because changes were applied
after I laid down the LINUXDOC_2_DOCBOOK tag.

Not everything was merged. In some cases, URLs had been shortened;

    http://www.freebsd.org/docproj/

becomes

     ../docproj/

This is a mistake, since users browsing the Handbook on their own machine
can't be expected to have links like this work. Of course, for mirrors,
they'll end up pointing back to the main site. For the mean time, do
nothing -- this will need an entity defined to reference the base URL
of the FreeBSD site, individual mirrors can set this as necessary.

Notice how some files (on the left) are merged to the same file (on
the right). This is because the new Handbook file structure is organised
on DocBook chapter lines.

Files with no revision number in the "From" column didn't exist when I
started the conversion.

File                 From  ->  To      Merged to files...
---------------------------------------------------------------
anoncvs.sgml               ->  1.1     cutting-edge/chapter.sgml
authors.sgml         1.93  ->  1.118   authors.ent
backups.sgml               ->  1.4     backups/chapter.sgml
bibliography.sgml    1.33  ->  1.37    bibliography/chapter.sgml
contrib.sgml         1.274 ->  1.312   staff/chapter.sgml
ctm.sgml             1.22  ->  1.23    cutting-edge/chapter.sgml
cvsup.sgml           1.36  ->  1.40    cutting-edge/chapter.sgml
disks.sgml                 ->  1.3     disks/chapter.sgml
eresources.sgml      1.39  ->  1.50    eresources/chapter.sgml
firewalls.sgml       1.19  ->  1.20    security/chapter.sgml
handbook.sgml        1.83  ->  1.91    handbook.sgml
history.sgml         1.24  ->  1.25    introduction/chapter.sgml
install.sgml         1.65  ->  1.67    install/chapter.sgml
isdn.sgml            1.12  ->  1.15    advanced-networking/chapter.sgml
kerberos.sgml        1.12  ->  1.13    security/chapter.sgml
kernelconfig.sgml    1.31  ->  1.32    kernelconfig/chapter.sgml
kerneldebug.sgml     1.17  ->  1.19    kerneldebug/chapter.sgml
linuxemu.sgml        1.22  ->  1.24    linuxemu/chapter.sgml
memoryuse.sgml       1.11  ->  1.12    internals/chapter.sgml
mirrors.sgml         1.80  ->  1.92    mirrors/chapter.sgml
nutshell.sgml        1.14  ->  1.15    introduction/chapter.sgml
pgpkeys.sgml         1.25  ->  1.28    pgpkeys/chapter.sgml
policies.sgml        1.16  ->  1.18    policies/chapter.sgml
porting.sgml         1.93  ->  1.112   contrib/chapter.sgml
ports.sgml           1.29  ->  1.31    ports/chapter.sgml
printing.sgml        1.21  ->  1.22    printing/chapter.sgml
relnotes.sgml        1.24  ->  1.28    introduction/chapter.sgml  [1]
submitters.sgml      1.161 ->  1.246   contrib/chapter.sgml
synching.sgml        1.12  ->  1.13    cutting-edge/chapter.sgml
userppp.sgml         1.28  ->  1.30    ppp-and-slip/chapter.sgml

[1] A chunk of relnotes.sgml is in an IGNORED marked section. Why?

Submitted by:	A bunch (~ 50%) of merging done by Charles A. Wimmer
                (cawimm@FreeBSD.ORG), rest by Nik.

    <xref linkend="target" remap="foo">

with

    <link linkend="target">foo</link>

Internal links within the Handbook now do the right thing.

Added

<!--
     Local Variables:
     mode: sgml
     sgml-declaration: "../chapter.decl"
     sgml-indent-data: t
     sgml-omittag: nil
     sgml-shorttag: nil
     sgml-always-quote-attributes: t
     sgml-minimize-attributes: max
     sgml-parent-document: ("../handbook.sgml" "part" "chapter")
     End:
-->

to the bottom of each chapter.sgml file so that Emacs can do the right
thing.

chapter.sgml in a directory named according to the value the id
attribute on that chapter.

Added chapters.ent, which lists the entities for each chapter.

Updated handbook.sgml to use these entities.