def post_update!(options = {})
      rsp = post(prepare_update_xml(options))
      success?(rsp.body) or log_error(rsp.body)
    end
def post_update!(options = {})
      rsp = post(prepare_update_xml(options))
      success?(rsp.body) or log_error(rsp.body)
    end
posts the buffer created by <tt>update</tt> to solr