RFR 8237218: Support NIST Curves verification in java implementation

[Weijun Wang]

Please take a review at

   http://cr.openjdk.java.net/~weijun/8237218/webrev.02/

A test is added that uses a patched ECDSASignature.java that exposes how the signature is verified.

BTW, I also updated ECDSASignature.java a little to accept non SunEC keys, so that I can do some interop testing. If you believe this is unnecessary I can revert the change.

Thanks,
Max