logpdf = new(lpdfvec, loglik, logpr)This is a class where each instance contains two lpdf 
instances and can be 
manipulated as a single instance.  It presumes both are based on the same
outermod instance, thus they share hyperparameters.  However
the model parameters are concatenated.  Currently also includes variations
on marginal adjustments.
Currently it is designed only for a pair, but the ordering is arbitrary.
Arguments
- loglik
 one reference to a
lpdfinstance- logpr
 another reference to a
lpdfinstance that sharesoutermodwithloglik
See also
base class: lpdf