Allow simple policy for bytes as well as unicode in python 2 and 3

src/AccessControl/SimpleObjectPolicies.py

@@ -86,7 +86,7 @@
 #        calling the function with the object and the attribute name.
 ContainerAssertions = {
     type(()): 1,
-    type(''): 1,
+    type(b''): 1,
     type(u''): 1,
     range: 1,
 }