Sanity checks for options needed for configfile mode.

def check_arguments(cls, conf):
        """
        Sanity checks for options needed for configfile mode.

        """
        try:
            # Check we have access to the config file
            f = open(conf['file'], "r")
            f.close()
        except IOError as e:
            raise ArgsError("Cannot open config file '%s': %s" %
                            (conf['file'], e))