'Helper method for prepare_server_https to figure out which new
listen statements need adding
:param set listens: Set of all needed Listen statements
:param list listens_orig: List of existing listen statements
:param string port: Port number we\'re adding'

def _add_listens(self, listens, listens_orig, port):

    if (port != '443'):
        port_service = ('%s    %s' % (port, 'https'))
    else:
        port_service = port
    new_listens = listens.difference(listens_orig)
    if ((port in new_listens) or (port_service in new_listens)):
        self.parser.add_dir_to_ifmodssl(parser.get_aug_path(self.parser.loc['listen']), 'Listen', port_service.split('    '))
        self.save_notes += ('Added    Listen    %s    directive    to    %s\n' % (port_service, self.parser.loc['listen']))
    else:
        for listen in new_listens:
            self.parser.add_dir_to_ifmodssl(parser.get_aug_path(self.parser.loc['listen']), 'Listen', listen.split('    '))
            self.save_notes += ('Added    Listen    %s    directive    to    %s\n' % (listen, self.parser.loc['listen']))
