Extend hardening against 'six' renames to include vendored version.

Forward-port bca6b38 from 2.13 branch.

src/App/ApplicationManager.py

@@ -152,7 +152,7 @@ def refcount(self, n=None, t=(type(Implicit), )):
         for m in sys.modules.values():
             if m is None:
                 continue
-            if m.__name__.startswith('six'):
+            if 'six.' in m.__name__:
                 continue
             for sym in dir(m):
                 ob = getattr(m, sym)