Merge branch 'rdikeshwar-2.13' into 2.13

doc/CHANGES.rst

@@ -8,6 +8,9 @@ http://docs.zope.org/zope2/
 2.13.24 (unreleased)
 --------------------
 
+- PR #51:  Harden debug control panel's module-crawling against trickery
+  performed by ``six``.
+
 - Issue #34: Fix ``NameError`` exception for ``WindowsError`` which could
   happen on non-windows systems.
 

src/App/ApplicationManager.py

@@ -163,6 +163,10 @@ class DebugManager(Item, Implicit):
         # return class reference info
         counts = {}
         for m in sys.modules.values():
+            if m is None:
+                continue
+            if m.__name__.startswith('six'):
+                continue
             for sym in dir(m):
                 ob = getattr(m, sym)
                 if type(ob) in t: