Permit Org.BouncyCastle.Crypto.Generators.ECKeyPairGenerator to save cur...

...ve names, per Jira BMA-101

When publicKeyParamSet is left null, then GenerateKeyPair() does not look up the parameter set to try to save the curve name.  When it's set, the constructor overloads for ECPublicKeyParameters and ECPrivateKeyParameters take the curve name and don't bother with explicit encoding.

This resolves Jira issue BMA-101.
This was another instance of checking the magnitude without checking the sign.  It's now logically consistent with ==.