replace no longer available meinproc with xsltproc

since the kdoctools removal meinproc is not available, replace
its usage in the macro for creating manual pages with xsltproc.
have in mind this is not tested and usually (from what I've seen)
xsltproc is executed like this:

xsltproc --path <resources dir> -nonet http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl <input> --output <output file>

in case this commit breaks something there will be a follow up but
since none of our components make use of it I will not bother much
for now.