def namespace_attributes(ns)
      Hash[ns.map do |prefix, uri|
             if prefix==""
               ["xmlns", uri]
             else
               [["xmlns", prefix].join(":"), uri]
             end
           end]
    end
def namespace_attributes(ns)
      Hash[ns.map do |prefix, uri|
             if prefix==""
               ["xmlns", uri]
             else
               [["xmlns", prefix].join(":"), uri]
             end
           end]
    end
produces a Hash of compact namespace attributes from a
 Hash of namespace bindings