The man pages generated by cp_debian_files.pl do not display correctly

In Koha Bug 27315 we dealt with the issue of man pages for the koha-* commands not displaying correctly.

This has now been fixed for the Debian packages, but is still an issue in koha-testing-docker because the xsltproc command in cp_debian_files.pl still uses the namespace-unaware DocBook XSL stylesheets.

I will submit a merge request that fixes this.