Squash a few calls to the hideously expensive PyObject_CallObject(o,a)

Squash a few calls to the hideously expensive PyObject_CallObject(o,a)
-- replace then with slightly faster PyObject_Call(o,a,NULL).  (The
difference is that the latter requires a to be a tuple; the former
allows other values and wraps them in a tuple if necessary; it
involves two more levels of C function calls to accomplish all that.)