[Python] Skip undeclared third bodies when adding Reactions

This needs to be the default behavior, since reactions can currently only be
added from the constructor.

interfaces/cython/cantera/_cantera.pxd

@@ -339,6 +339,7 @@ cdef extern from "cantera/kinetics/Kinetics.h" namespace "Cantera":
 
         void addPhase(CxxThermoPhase&) except +
         void init() except +
+        void skipUndeclaredThirdBodies(cbool)
         void addReaction(shared_ptr[CxxReaction]) except +
         void finalize() except +
 

interfaces/cython/cantera/base.pyx

@@ -99,6 +99,7 @@ cdef class _SolutionBase:
             for phase in phases:
                 self.kinetics.addPhase(deref(phase.thermo))
             self.kinetics.init()
+            self.kinetics.skipUndeclaredThirdBodies(True)
             for reaction in reactions:
                 self.kinetics.addReaction(reaction._reaction)
             self.kinetics.finalize()