* src/ocsp.h (struct ocsp_reqitem_s): Increase size of hash items.
(struct ksba_ocsp_s): Add flag sha256_certid.
* src/ocsp.c (oidstr_sha256): New.
(ksba_ocsp_set_nonce): Add hack to set/clear this flag.
(issuer_name_hash): Add arg use_sha256 and change accordingly.
(issuer_key_hash): Ditto.
(ksba_ocsp_prepare_request): Make use of the new flag.
(parse_single_response): Allow the use of SHA256 CertID items.
* tests/sha1.c (sha256_hash_buffer): New.  Also add a bunch of othe
functions to implement SHA256.
* tests/t-ocsp.c (sha256_certid): New flag.
(one_request): Use it.
(one_response): Ditto.
(my_hash_buffer): Support SHA256.
(main): Add option --sha256.