[Bf-python] Callback types (sorry, got things wrong)

[Yann Vernier]

My apologies. Please ignore my thoughts on return values, they were from
thinking the call back would occur within the call receiving the
callback as an argument. I retract that mess, leaving only this snippet
for adaptation to the callback translation code:

  PyObject *retval;

  retval=...Call...;
  if(retval)
    Py_DECREF(retval);
  else
    PyErr_Print();

This will print any exceptions that occur, although it should perhaps
tell why the function was called too.