fixed some NameErrors

--HG--
branch : trunk
diff --git a/jinja2/nodes.py b/jinja2/nodes.py
index f87bbb8..c1231ea 100644
--- a/jinja2/nodes.py
+++ b/jinja2/nodes.py
@@ -504,7 +504,8 @@
         if self.ctx != 'load':
             raise Impossible()
         try:
-            return environmen.subscribe(self.node.as_const(), self.arg.as_const())
+            return self.environment.subscribe(self.node.as_const(),
+                                              self.arg.as_const())
         except:
             raise Impossible()