crypto/x509: get hash information from signatureAlgorithmDetails and check that it matches

signatureAlgorithmDetails already knows the hash function for each
signature algorithm so there's no point in duplicating that. Also, check
that the public key type of the signature algorithm actually matches the
given public key.

Change-Id: I7aab4ea71691fb815d67ba790b721ce02de11b85
Reviewed-on: https://go-review.googlesource.com/57211


Reviewed-by: Adam Langley <agl@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>