X509::CRL's signature_algorithm is "itu-t" by default
more (MRI) compatibility when accesing cert.public_key
finish/review X509::Revoked's API
warn when getExtensionValue returns null (we might not work as expected)
improve (latest) MRI compatibility
use our shared helper factory method to create a new extension
simplify DERUTCTime to Ruby Time conversion
fallback to "global" ASN1 name registry if not found in runtime specific registry