docs: don't download DTDs when building docs Fixes: | xsltproc /usr/share/xml/docbook/stylesheet/nwalsh/manpages/docbook.xsl `echo grml-crypt.8.txt |sed -e 's/.txt/.xml/'` | error : Resource temporarily unavailable | grml-crypt.8.xml:2: warning: failed to load external entity "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" | D DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" | ^ | Note: Writing grml-crypt.8