G _MUST_ be always n+1 to make the threshold encryption algorithm safe. We assume G=n+1 both for standard and threshold version.
G is no longer a parameter of PublicKey.
We don't need G for our PublicKey since it's now always equal N+1. It's required by the `ThresholdKey` to compile, so I moved it there. I will investigate if for a threshold Paillier scheme G is really needed in the pkey.
Piotr Dyraga