* mkerrors: Prettier error formating for gpg-error style codes.
* conversion.c (_gpgme_parse_timestamp): New. Now also handles ISO
8601 timestamps as used by gnupg 1.9.2.
* keylist.c (parse_timestamp): Removed. Replaced calls by
_gpgme_parse_timestamp.
* verify.c (_gpgme_verify_status_handler): Replaced strtoul by
_gpgme_parse_timestamp.
* sign.c (append_xml_siginfo): Ditto.