JDK 9 Review Request for 8038349: Signing XML with DSA throws Exception when key is larger than 1024 bits

[Sean Mullan]

Please review the following change which adds support for 2048-bit DSA 
keys and the DSA-SHA256 algorithm to the XML Signature implementation:

webrev: http://cr.openjdk.java.net/~mullan/webrevs/8038349/webrev.00/

JDK 8 already includes the underlying support for both of these in the 
Sun provider. For 2048 bit keys, the ASN.1 parsing code in the XML 
Signature layer needed to be adapted to handle 2048 bit keys, and for 
SHA-256 it was just a matter of registering the algorithm URI and 
instantiating a Signature object with the SHA256WithDSA algorithm.

Thanks,
Sean