Tokenizer1: Fix order in which ellipsis pattern appears.
Make Model.factors(Iterable[Var]) the abstract base case rather than
Model.factors(Var).  This will enable more succinct efficient overriding
of Model unrolling.
Note that I have temporarily commented out the test for
DualDecomposition.  I'm getting an infinite loop somewhere I can't find.
Remove InferByEM.  Just use EMInferencer instead.