Add RR Type ZONEMD to RR definitions.

on unit tests.

…nal.

and nsec3 bitmap checks.

zonemd, unit test for dnssec verify function test harness.

…onemd

zonemd, unit test of nsec and nsec3 denial.

…zone.

…e if
no ZONEMD is present.

…DNSSEC.

zonemd, fix clang analyzer warning about null nsec3 salt pointer access.

… and not
written to file.

zone is written after axfr, but before check.  But zone is then rejected
after check completes..

permissive mode for zonemd.

…put.

…slands.

- Merge PR #317: ZONEMD Zone Verification, with RFC 8976 support.
  ZONEMD records are checked for zones loaded as auth-zone,
  with DNSSEC if available.  There is an added option
  zonemd-permissive-mode that makes it log but not fail wrong zones.
  With zonemd-reject-absence for an auth-zone the presence of a
  zonemd can be mandated for specific zones.