Simplify and speedup uses of Py_BuildValue():

* Py_BuildValue("(OOO)",a,b,c)  -->  PyTuple_Pack(3,a,b,c)
* Py_BuildValue("()",a)         -->  PyTuple_New(0)
* Py_BuildValue("O", a)         -->  Py_INCREF(a)

Modules/cStringIO.c

@@ -439,7 +439,7 @@ O_writelines(Oobject *self, PyObject *args) {
         tmp = PyObject_CallFunction(joiner, "O", args);
         UNLESS (tmp) return NULL;
 
-        args = Py_BuildValue("(O)", tmp);
+        args = PyTuple_Pack(1, tmp);
         Py_DECREF(tmp);
         UNLESS (args) return NULL;