gpg: Fix the encrypt+sign hash algo preference selection for ECDSA.
* g10/keydb.h (pref_hint): Change from union to struct and add field 'exact'. Adjust callers. * g10/pkclist.c (algo_available): Take care of the exact hint. * g10/sign.c (sign_file): Rework the hash detection from recipient prefs.
This fixes a encrypt+sign case like: One recipient key has SHA512 as
highest ranked hash preference but the the signing key is a 256 bit
curve. Because we don't want to use a truncated hash with ECDSA, we
need to have an exact match - this is in particular important for
smartcard which check that the hash matches the curves.
- Signed-off-by: Werner Koch <email@example.com>