OS/400 crypto library is unable to sign a precomputed SHA1 hash: however
it does support a procedure that hashes data fragments and rsa signs.
If defined, the new macro _libssh2_rsa_sha1_signv() implements this function
and disables use of _libssh2_rsa_sha1_sign().
The function described above requires that the struct iovec unused slacks are
cleared: for this reason, macro libssh2_prepare_iovec() has been introduced.
It should be defined as empty for crypto backends that are not sensitive
to struct iovec unused slack values.
Implement support for these algorithms and wire them up to the libgcrypt
and OpenSSL backends. Increase the maximum MAC buffer size to 64 bytes
to prevent buffer overflows. Prefer HMAC-SHA-256 over HMAC-SHA-512, and
that over HMAC-SHA-1, as OpenSSH does.
Closes#40
Initially reported by Bob Kast as "Wincng - define function
prototypes for wincng routines". Thanks a lot.
Also replaced structure definitions with type definitions.
Removed header file combination that is not supported on a real
Windows platform and can only be compiled using MinGW. Replaced
custom NTSTATUS return code checks with BCRYPT_SUCCESS macro.
