def addListing(parser):
    """
    Add option to request the list of versions.
    """
    parser.add_option('-l', '--list', action='store_true', help=
        'list the available versions of the requested project and exit')
    parser.add_option('--list-versions', action='store_true', dest='list',
        help='obsolete spelling of --list', default=False)
    parser.add_option('-L', '--list-platforms', action='store_true', help=
        'list the available platforms for the requested project/version and exit'
        )
    parser.set_defaults(list=False, list_platforms=False)
    return parser
