SF #561244, Micro optimizations

Initialize the small integers and __builtins__ in startup.
This removes some if conditions.
Change XDECREF to DECREF for values which shouldn't be NULL.
diff --git a/Include/intobject.h b/Include/intobject.h
index ab936b2..50e6a73 100644
--- a/Include/intobject.h
+++ b/Include/intobject.h
@@ -30,6 +30,7 @@
 #define PyInt_Check(op) PyObject_TypeCheck(op, &PyInt_Type)
 #define PyInt_CheckExact(op) ((op)->ob_type == &PyInt_Type)
 
+PyAPI_FUNC(int) PyInt_Init(void);
 PyAPI_FUNC(PyObject *) PyInt_FromString(char*, char**, int);
 #ifdef Py_USING_UNICODE
 PyAPI_FUNC(PyObject *) PyInt_FromUnicode(Py_UNICODE*, int, int);