don't use a slot wrapper from a different special method (closes #14658)

This also alters the fix to #11603. Specifically, setting __repr__ to
object.__str__ now raises a recursion RuntimeError when str() or repr() is
called instead of silently bypassing the recursion. I believe this behavior is
more correct.
diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py
index 28dfbff..b66849e 100644
--- a/Lib/test/test_descr.py
+++ b/Lib/test/test_descr.py
@@ -4591,7 +4591,15 @@
             pass
         Foo.__repr__ = Foo.__str__
         foo = Foo()
-        str(foo)
+        self.assertRaises(RuntimeError, str, foo)
+        self.assertRaises(RuntimeError, repr, foo)
+
+    def test_mixing_slot_wrappers(self):
+        class X(dict):
+            __setattr__ = dict.__setitem__
+        x = X()
+        x.y = 42
+        self.assertEqual(x["y"], 42)
 
     def test_cycle_through_dict(self):
         # See bug #1469629