Added ScalarProdUpdate operator.

Handles the cases which, in the python simulator, are handled by
reshaping the dot product with ``reshape_dot''. Basically, whenever
A is a scalar.
Made operator data members protected
Can now handle PyFuncs that return scalars.
Small fixes to simulator.py
Added ScalarDotInc operator.
Can now handle scalar B in ProdUpdate.
First pass at probe system.