exclude PyLong optimisation for arithmetic operators in Py2.7 as it's actually...

exclude PyLong optimisation for arithmetic operators in Py2.7 as it's actually unlikely that we'd encounter C long sized PyLong objects in Py2.x (which has the 'int' type for that)

Cython/Utility/Optimize.c

@@ -557,7 +557,7 @@ static PyObject* __Pyx_PyInt_{{op}}{{order}}(PyObject *op1, PyObject *op2, CYTHO
     }
     #endif
 
-    #if CYTHON_USE_PYLONG_INTERNALS
+    #if CYTHON_USE_PYLONG_INTERNALS && PY_MAJOR_VERSION >= 3
     if (likely(PyLong_CheckExact({{pyval}}))) {
         const long {{'a' if order == 'CObj' else 'b'}} = intval;
         long x, {{ival}};
@@ -661,7 +661,7 @@ static PyObject* __Pyx_PyFloat_{{op}}{{order}}(PyObject *op1, PyObject *op2, dou
     #endif
 
     if (likely(PyLong_CheckExact({{pyval}}))) {
-        #if CYTHON_USE_PYLONG_INTERNALS
+        #if CYTHON_USE_PYLONG_INTERNALS && PY_MAJOR_VERSION >= 3
         const digit* digits = ((PyLongObject*){{pyval}})->ob_digit;
         const Py_ssize_t size = Py_SIZE({{pyval}});
         switch (size) {