Make DocBook sources namespaced again

Make DocBook sources namespaced again

Every DocBook source document can be namespaced (DocBook 5) or
non-namespaced (DocBook 4).  The set of XSL stylesheets used for
producing an output document can also be namespaced or non-namespaced.
Namespaced source documents should be used with namespaced stylesheets
and non-namespaced source documents should be used with non-namespaced
stylesheets.  However, both stylesheet flavors contain processing rules
which allow them to be used interchangeably for any type of source
document.

Unfortunately, these processing rules became broken in version 1.79.1 of
the stylesheets, which means that non-namespaced source documents can no
longer be correctly transformed into man pages using namespaced
stylesheets and vice versa.  This problem was fixed upstream [1], but no
released version of the XSL stylesheets contains that fix yet.

Back in 2016, this problem was reported as RT #43831 and allegedly fixed
in commit 1b8ce3b3302f0afe682d04df8a1f20b4ac346fb2.  However, that fix
only helped for the non-namespaced version of the stylesheets - while
also breaking man page generation for the namespaced flavor.

Since using namespaced DocBook sources is the current best practice
(DocBook 5), make BIND DocBook sources namespaced again.  When using
version 1.79.1 or 1.79.2 of the XSL stylesheets, care must be taken to
ensure namespaced stylesheets are used for generating BIND
documentation.

[1] https://github.com/docbook/xslt10-stylesheets/issues/109