Add RSA_check_key function.

This is function that is available in OpenSSL too. Here it only returns
zero or one and doesn't do expensive primality checks on p and q.

https://code.google.com/p/chromium/issues/detail?id=396250

Change-Id: I7a173da26e06440dbb595fb717e3a620edf23576
Reviewed-on: https://boringssl-review.googlesource.com/1334
Reviewed-by: Adam Langley <agl@google.com>
4 files changed