* cipher/dsa-common (_gcry_dsa_normalize_hash): New. Truncate opaque
  mpis as required for DSA and ECDSA signature schemas.
* cipher/dsa.c (verify): Return gpg_err_code_t value from verify() to
  behave like the rest of internal sign/verify functions.
* cipher/dsa.c (sign, verify, dsa_verify): Factor out hash truncation.
* cipher/ecc-ecdsa.c (_gcry_ecc_ecdsa_sign): Factor out hash truncation.
* cipher/ecc-ecdsa.c (_gcry_ecc_ecdsa_verify):
  as required by ECDSA scheme, truncate hash values to bitlength of
  used curve.
* tests/pubkey.c (check_ecc_sample_key): add a testcase for hash
  truncation.