Includes checks for 64-bit file structure and avoids repeating header 
checks.

This is needed so that the new transacted type will be able to easily support
this logic.

This is to avoid accessing the top-level StorageImpl directly.

Since simple mode does not support substorages, we know these are the same.

cryptnet: Implement getting the certificate issuer URL from a cert's authority info access extension.

cryptnet: Add tests for getting the certificate issuer URL from a cert's authority info access extension.