[CFR] Migrating the documentation to a real XML toolchain

[Gabor Kovesdan]

Hi,

I have some improvements for the doc infrastructures in the xml-tools 
branch. I think that the changeset is now getting mature enough to be 
merged back so I'd like to ask for review. It does not affect the web 
pages, only books and articles. The rendered docs are available at:
http://people.freebsd.org/~gabor/db45/

For every article/book, you will find there the chunked XHTML docs or if 
you manually enter the URL, you can access the single XHTML and PDF 
versions as (article|book)\.(html|pdf).

The branch contains the following changes:
- Upgrade to DocBook 4.5
- Use XSLT instead of DSSSL to render XHTML-based output
- Fix make lint and validate the whole documentation set
- Add support for XInclude in DocBook documents
- Add experimental epub support
- Add experimental support for XSL-FO-based printed output
- Clean up obsolete SGML constructs
- Clean up catalogs
- Drop HTML Tidy since it is not needed any more

To build the branch manually, you need docbook-450 apart from the usual 
docproj stuff. However, several dependencies are not needed any more and 
will be dropped later from the docproj port, namely:
- textproc/opensp
- www/tidy-lib
- textproc/html
- textproc/linuxdoc
- textproc/docbook-xml

Please let me know about bugs, comments, ideas, etc.

Thanks,
Gabor