Added testcase for a bug

--HG--
branch : trunk
diff --git a/jinja2/compiler.py b/jinja2/compiler.py
index 6b9c786..36f55a9 100644
--- a/jinja2/compiler.py
+++ b/jinja2/compiler.py
@@ -595,7 +595,9 @@
         # variables that are undeclared (accessed before declaration) and
         # declared locally *and* part of an outside scope raise a template
         # assertion error. Reason: we can't generate reasonable code from
-        # it without aliasing all the variables.  XXX: alias them ^^
+        # it without aliasing all the variables.
+        # this could be fixed in Python 3 where we have the nonlocal
+        # keyword or if we switch to bytecode generation
         overriden_closure_vars = (
             func_frame.identifiers.undeclared &
             func_frame.identifiers.declared &