Use DocBook XSL stylesheets for man page building

Use DocBook XSL stylesheets for man page building

This switches the man page building process to use the DocBook XSL stylesheet
toolchain.  The previous targets for Docbook2X are removed. configure has been
updated to look for the new tools.  The Documentation appendix contains the
new build instructions.  There are also a few isolated tweaks in the
documentation to improve places that came out strangely in the man pages.