improve abstract property support (closes #11610)
Thanks to Darren Dale for patch.
diff --git a/Include/object.h b/Include/object.h
index 3cd5297..1666271 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -473,6 +473,7 @@
PyAPI_FUNC(PyObject *) PyObject_GetAttr(PyObject *, PyObject *);
PyAPI_FUNC(int) PyObject_SetAttr(PyObject *, PyObject *, PyObject *);
PyAPI_FUNC(int) PyObject_HasAttr(PyObject *, PyObject *);
+PyAPI_FUNC(int) _PyObject_IsAbstract(PyObject *);
PyAPI_FUNC(PyObject *) _PyObject_GetAttrId(PyObject *, struct _Py_Identifier *);
PyAPI_FUNC(int) _PyObject_SetAttrId(PyObject *, struct _Py_Identifier *, PyObject *);
PyAPI_FUNC(int) _PyObject_HasAttrId(PyObject *, struct _Py_Identifier *);