lint improvements

Add asn_backwards_compat to check backwards compat between two ASN.1 files, and check_asn_backwards_compat to run that between various 33.128 releases of TS33128Payloads.

Add more checks to lint_asn: check XIRIEvent versus IRIEvent tags to ensure the same field names and type exist at a tag; check if a type (e.g., SEQUENCE) has "holes" in the tag numbering.