* g10/tdbdump.c (export_ownertrust): Skip records marked with the
option --trusted-key.
(import_ownertrust): Clear the trusted-key flag.
* g10/tdbio.h (struct trust_record): Add field flags.
* g10/tdbio.c (tdbio_dump_record): Improve output.
(tdbio_read_record, tdbio_write_record): Handle flags.
* g10/trustdb.c (verify_own_keys): Clear stale trusted-keys and set
the flag for new --trusted-keys.
(tdb_update_ownertrust): Add arg as_trusted_key.  Update callers.