Add diff support for other files types and directories

[lowell80]

def do_diff(args):
    ''' Compare two configuration files. '''
    # Todo:  Allow fallback to text comparisons for non-conf files.
    # Todo:  Eventually support directory (or recursive?) diffs too.
    parse_args = dict(dup_stanza=args.duplicate_stanza, dup_key=args.duplicate_key,
                      keep_comments=args.comments, strict=True)
    # Parse all config files
    try:
        cfg1 = parse_conf(args.conf1, **parse_args)
        cfg2 = parse_conf(args.conf2, **parse_args)
    except IOError, e:
        sys.stderr.write("Unable to open conf file.  {}\n".format(e.message))
        return EXIT_CODE_NO_SUCH_FILE
    except ConfParserException, e:
        sys.stderr.write("Unable to parse conf file.  {}\n".format(e))
        # We don't distinguish between bad conf files and safety checks here.
        return EXIT_CODE_BAD_CONF_FILE
    diffs = compare_cfgs(cfg1, cfg2)
    rc = show_diff(args.output, diffs, headers=(args.conf1, args.conf2))
    if rc == EXIT_CODE_DIFF_EQUAL:
        sys.stderr.write("Files are the same.\n")
    elif rc == EXIT_CODE_DIFF_NO_COMMON:
        sys.stderr.write("No common stanzas between files.\n")
    return rc