'Return a comma-separated list of option strings and metavars.
:param option:  tuple of (short opt, long opt), e.g: (\'-f\', \'--format\')
:param mvarfmt: metavar format string - evaluated as mvarfmt % metavar
:param optsep:  separator'

def _format_option_strings(self, option, mvarfmt='    <%s>', optsep=',    '):

    opts = []
    if option._short_opts:
        opts.append(option._short_opts[0])
    if option._long_opts:
        opts.append(option._long_opts[0])
    if (len(opts) > 1):
        opts.insert(1, optsep)
    if option.takes_value():
        metavar = (option.metavar or option.dest.lower())
        opts.append((mvarfmt % metavar.lower()))
    return ''.join(opts)
