(time): Declare if not defined.

(time): Declare if not defined.
(base_64_digits): Moved here from create.c.
(base64_map): Use UCHAR_MAX for size, not less-clear (unsigned char) -1.
(read_and): Don't get time from header unless we need it now;
as getting time can cause duplicate diagnostics if bogus.
Remove "Hmm, " from diagnostic.
Use "Skipping to next header" uniformly.
(from_header): Renamed from from_chars.  All uses changed.
Allow different forms for unportable 2's complement numbers.
Don't check for extended forms when parsing checksums.
Parse base-256 output.
(gid_from_header): Renamed from gid_from_chars.  All uses changed.
(major_from_header): Renamed from major_from_chars.  All uses changed.
(minor_from_header): Renamed from minor_from_chars.  All uses changed.
(mode_from_header): Renamed from mode_from_chars.  All uses changed.
(off_from_header): Renamed from off_from_chars.  All uses changed.
(size_from_header): Renamed from size_from_chars.  All uses changed.
(time_from_header): Renamed from time_from_chars.  All uses changed.
Warn about future timestamps.
(uid_from_header): Renamed from uid_from_chars.  All uses changed.
(uintmax_from_header): Renamed from uintmax_from_chars.  All uses changed.
(tartime): New function, incorporating isotime.
(isotime): Delete.
(print_header): Use tartime.