Implement EVP_PKEY_supports_digest in Windows EVP_PKEY wrappers.

Implement EVP_PKEY_supports_digest in Windows EVP_PKEY wrappers.

This allows BoringSSL's SSL implementation to account for the CNG
or CAPI provider's capabilities when choosing a hash to sign. Per
the fixes in https://crbug.com/278370, we assume CAPI keys and CNG
RSA keys of size 1024-bit or below can only support SHA-1.

This also prevents BoringSSL from choosing SHA-224 which we can't
sign with CNG either.

BUG=418822
Committed: https://crrev.com/2a5e750faa7a7bd8ee6635f208e509e792cdd70a
Cr-Commit-Position: refs/heads/master@{#305920}

[davidben, 2014-11-14 22:47:47]

davidben@chromium.org changed reviewers:
+ rsleevi@chromium.org

[davidben, 2014-11-14 22:47:47]

This depends on the other client auth CL and the tower of changes ending at, but
this is what I was referring to about hash function stuff.

https://boringssl-review.googlesource.com/#/c/2280/

I wasn't able to get NCryptIsAlgSupported to work, so this is implementing the
same heuristic we had before.

[Ryan Sleevi, 2014-11-22 01:08:45]

lgtm

[davidben, 2014-11-26 22:41:28]

The CQ bit was checked by davidben@chromium.org

[commit-bot: I haz the power, 2014-11-26 22:42:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/731673002/40001

[commit-bot: I haz the power, 2014-11-27 00:03:15]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2014-11-27 00:04:07]

Patchset 3 (id:??) landed as
https://crrev.com/2a5e750faa7a7bd8ee6635f208e509e792cdd70a
Cr-Commit-Position: refs/heads/master@{#305920}