* packet.h, trustdb.h, trustdb.c (trust_string): New. Return a string

like "fully trusted", "marginally trusted", etc. (get_min_ownertrust):
New.  Return minimum ownertrust. (update_min_ownertrust): New.  Set
minimum ownertrust. (check_regexp): New.  Check a regular epression
against a user ID. (ask_ownertrust): Allow specifying a minimum value.
(get_ownertrust_info): Follow the minimum ownertrust when returning a
letter. (clear_validity): Remove minimum ownertrust when a key becomes
invalid. (release_key_items): Release regexp along with the rest of the
info. (validate_one_keyblock, validate_keys): Build a trust sig chain
while validating.  Call check_regexp for regexps.  Use the minimum
ownertrust if the user does not specify a genuine ownertrust.

* pkclist.c (do_edit_ownertrust): Only allow user to select a trust level
greater than the minimum value.

* parse-packet.c (can_handle_critical): Can handle critical trust and
regexp subpackets.

* trustdb.h, trustdb.c (clear_ownertrusts), delkey.c (do_delete_key),
import.c (import_one): Rename clear_ownertrust to clear_ownertrusts and
have it clear the min_ownertrust value as well.

* keylist.c (list_keyblock_print): Indent uid to match pub and sig.

g10/packet.h

@@ -212,6 +212,10 @@ typedef struct {
     PKT_user_id *user_id;   /* if != NULL: found by that uid */
     struct revocation_key *revkey;
     int     numrevkeys;
+    u32     trust_timestamp;
+    byte    trust_depth;
+    byte    trust_value;
+    const byte *trust_regexp;
     MPI     pkey[PUBKEY_MAX_NPKEY];
 } PKT_public_key;