FIX: eqcalculate: Compute degrees of freedom correctly when only a subset of constituents in a phase's sublattice model are used in a calculation.
FIX: eqcalculate: Compute degrees of freedom correctly when only a subset of constituents in a phase's sublattice model are used in a calculation.

tkphd/pycalphad,tkphd/pycalphad,tkphd/pycalphad