[9] Request for Review: 8046724: XML Signature ECKeyValue elements cannot be marshalled or unmarshalled

[Jason Uh]

Please review this fix, which allows XML Signature ECKeyValue elements 
to be marshalled and unmarshalled.

Dependence on internal sun.security.* classes has been removed, so that 
the (un)marshalling can happen without reflection.

webrev: http://cr.openjdk.java.net/~juh/8046724/00/
bug: https://bugs.openjdk.java.net/browse/JDK-8046724

A corresponding test will be added to the closed repository.

Thanks,
Jason