[pkg] various fixes - add missing files to MANIFEST - exclude doc/changes from dh_installchangelogs (it's a directory, which dh_installchangelogs doesn't expect) - fix doc build in debian package

version=3
opts=uversionmangle=s/(rc|a|b|c)/~$1/ \
http://pypi.debian.net/cubicweb/cubicweb-(.+)\.(?:zip|tgz|tbz|txz|(?:tar\.(?:gz|bz2|xz)))