separate downloading of Unicode property files and auxiliary files

        Separate downloading of Unicode property files in ucd and in ucd/auxiliary.
        This is needed because we need information from separate index.html files
        to discover the exact file names of property files during a beta period.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_6@67562 b2dd03c8-39d4-4d8f-98ff-823fe69b080e