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)

Python/exceptions.c

@@ -1821,7 +1821,7 @@ _PyExc_Init(void)
     }
 
     /* Now we need to pre-allocate a MemoryError instance */
-    args = Py_BuildValue("()");
+    args = PyTuple_New(0);
     if (!args ||
 	!(PyExc_MemoryErrorInst = PyEval_CallObject(PyExc_MemoryError, args)))
     {