Set OPENSSL_EC_NAMED_CURVE on our EC_KEY instances

This means any X.509 certs generated from our keys will be encoded
along with the curve OID so that we can still load them afterwards.

http://wiki.openssl.org/index.php/Elliptic_Curve_Cryptography#Named_Curves
NameError here, `ec_data` is the parameter, this is `ec_cdata`.