* g10/free-packet.c (copy_public_key): Factor some code out to ...
(copy_public_key_basics): new.
* g10/build-packet.c (build_sig_subpkt_from_sig): New arg signhints.
* g10/packet.h (PUBKEY_USAGE_RENC): Fix value.
(SIGNHINT_KEYSIG, SIGNHINT_SELFSIG): Moved from sign.c.
(SIGNHINT_ADSK): New.
(PKT_public_key): Change pubkey_usage from byte to u16.
(PKT_user_id): Cosmetic fix: change help_key_usage from int to u16.
* g10/getkey.c (parse_key_usage): Make public.
* g10/misc.c (openpgp_pk_algo_usage): Take PUBKEY_USAGE_RENC in
account.
* g10/sign.c (update_keysig_packet): Set SIGNHINT_ADSK.
(make_keysig_packet): Ditto.
(do_sign): No time warp check in ADSK mode.
* g10/sig-check.c (check_signature_metadata_validity): Ditto.
* g10/keygen.c (struct opaque_data_usage_and_pk): Remove.
(write_keybinding): Do not use the removed struct.
(do_add_key_flags): Support PUBKEY_USAGE_RENC and others.
(keygen_add_key_flags_and_expire): Rewrite and make public.
* g10/keyedit.c (enum cmdids): Add cmdADDADSK.
(keyedit_menu): Add command "addadsk".
(menu_addadsk): New.

The "restricted encryption key" (2nd,0x04) does not take part in any
automatic selection of encryption keys.  It is only found on a
subkey signature (type 0x18), one that refers to the key the flag
applies to.