less aggressive callable() optimisation in Py2

Cython/Utility/ObjectHandling.c

@@ -435,7 +435,7 @@ static CYTHON_INLINE int __Pyx_TypeTest(PyObject *obj, PyTypeObject *type) {
 
 /////////////// CallableCheck.proto ///////////////
 
-#if CYTHON_COMPILING_IN_CPYTHON
+#if CYTHON_COMPILING_IN_CPYTHON && PY_MAJOR_VERSION >= 3
 #define __Pyx_PyCallable_Check(obj)   ((obj)->ob_type->tp_call != NULL)
 #else
 #define __Pyx_PyCallable_Check(obj)   PyCallable_Check(obj)

tests/run/builtin_callable.pyx

@@ -10,6 +10,13 @@ def test_callable(x):
     False
     >>> test_callable('ABC')
     False
+
+    >>> class C: pass
+    >>> test_callable(C)
+    True
+    >>> test_callable(C())
+    False
+
     >>> test_callable(int)
     True
     >>> test_callable(test_callable)