scd: ECDH Support.
* agent/divert-scd.c (divert_pkdecrypt): Support ECDH. * scd/app-openpgp.c (get_algo_byte, store_fpr): Support ECDH. (send_key_attr): Support ECDH. Fix EdDSA algorithm value. (retrieve_key_material): Initialize fields. (get_public_key, ecc_writekey, do_writekey): Support ECDH. (ecdh_writekey): Remove. (do_decipher): Support ECDH. (parse_algorithm_attribute): Support ECDH. Fix EdDSA.
Following the gpg-agent protocol, SCDaemon's counter part is now
implemented.