PR/50360: Thomas Klausner: MKREPRO fix

Fix the index building which got completely broken after the last update.

branches: 1.4.4;
Reorg docs, part 2:
Rename the following reference documents to match their programs:
shell -> sh
viref -> vi

and rename the following to match their topic better:
ipctut -> sockets
ipc -> sockets-advanced

Also, the old "timed" and "timedop" docs are now ref5/timed and
ref8/timed respectively, as the first of these documented the
protocol.

Reorg docs, part 1:
Move all the reference manuals to subdirs of /usr/share/doc/reference.
We have subdirs ref1-ref9, corresponding to man page sections 1-9.

Everything that's the reference manual for a program (sections 1, 6,
8), C interface (sections 2, 3), driver or file system (section 4),
format or configuration (section 5), or kernel internal interface
(section 9) belongs in here.

Section 7 is a little less clear: some things that might go in section
7 if they were a man page aren't really reference manuals. So I'm only
putting things in reference section 7 that are (to me) clearly
reference material, rather than e.g. tutorials, guides, FAQs, etc.
This obviously leaves some room for debate, especially without first
editing the docs with this distinction in mind, but if people hate
what I've done things can always be moved again.

Note also that while roff macro man pages traditionally go in section
7, I have put all the roff documentation (macros, tools, etc.) in one
place in reference/ref1/roff. This will make it easier to find and
also easier to edit it into some kind of coherent form.

Rework /usr/share/doc.

Update the <bsd.doc.mk> infrastructure, and update the docs to match
the new infrastructure.

- Build and install text, ps, pdf, and/or html, not roff sources.

- Don't wire the chapter numbers into the build system, or use them in
the installed pathnames. This didn't matter much when the docs were a
museum, but now that we're theoretically going to start maintaining
them again, we're going to add and remove documents periodically and
having the chapter numbers baked in creates a lot of thrashing for no
purpose.

- Specify the document name explicitly, rather than implicitly in a
path. Use this name (instead of other random strings) as the name
of the installed files.

- Specify the document section, which is the subdirectory of
/usr/share/doc to install into.

- Allow multiple subdocuments. (That is, multiple documents in one
output directory.)

- Enumerate the .png files groff emits along with html so they can be
installed.

- Remove assorted hand-rolled rules for running roff and roff widgetry
and add enough variable settings to make these unnecessary. This
includes support for
- explicit use of soelim
- refer
- tbl
- pic
- eqn

- Forcibly apply at least minimal amounts of sanity to certain
autogenerated roff files.

- Don't exclude USD.doc, SMM.doc, and PSD.doc directories from the
build, as they now actually do stuff.

Note: currently we can't generate pdf. This turns out to be a
nontrivial problem with no immediate solution forthcoming. So for now,
as a workaround, install compressed .ps as the printable form.

branches: 1.1.2; 1.1.4;
Add build glue and docs