Compatibility with docbook-xsl 1.79.2 and later

[rdmark]

From docbook-xsl 1.79.2 onwards, the project introduced new namespacing and canonical URL to their own CDN that breaks compatibility with our manpage sources.

See upstream bug: docbook/xslt10-stylesheets#65

This breaks the compatibility with our local stylesheets man.xsl / html.xsl which leads to some minor breakage, notably the mapping of refentry.version and refentry.date.

The current workaround is to use v1.79.1 which was the last that used the old namespace and sourceforge CDN.

[rdmark]

Interestingly, Debian is distributing a non-namespaced version of 1.79.2 docbook-xsl (compatible with our man page sources) in addition to the namespaced docbook-xsl-ns (not compatible). I read that macports is doing something similar. Others may too.

[rdmark]

Discarding this. The non-namespaced edition of docbook is not going away, and we don't need the new features of later editions.