Prepare for a forthcoming new algorithm id.
* include/cipher.h (PUBKEY_ALGO_ECC): New. * g10/keyid.c (pubkey_letter): Add letter 'C'.
ID 22 will be used for generic ECC, i.e. one which can be used for
ECDSA and ECDH. The only support in 1.4 will pretty printing the
algorithm id.