Fixed a small bug with the undefined object: the error message on divisions with undefined objects was misleading.

--HG--
branch : trunk
diff --git a/jinja2/sandbox.py b/jinja2/sandbox.py
index e9ab1d9..7b28273 100644
--- a/jinja2/sandbox.py
+++ b/jinja2/sandbox.py
@@ -212,14 +212,14 @@
             value = getattr(obj, attribute)
         except AttributeError:
             try:
-                return obj[argument]
+                return obj[attribute]
             except (TypeError, LookupError):
                 pass
         else:
             if self.is_safe_attribute(obj, attribute, value):
                 return value
             return self.unsafe_undefined(obj, attribute)
-        return self.undefined(obj=obj, name=argument)
+        return self.undefined(obj=obj, name=attribute)
 
     def unsafe_undefined(self, obj, attribute):
         """Return an undefined object for unsafe attributes."""