make this work with py2.5
diff --git a/Parser/asdl_c.py b/Parser/asdl_c.py
index d9d7662..b4c31c3 100755
--- a/Parser/asdl_c.py
+++ b/Parser/asdl_c.py
@@ -1,5 +1,6 @@
 #! /usr/bin/env python
 """Generate C code from an ASDL description."""
+from __future__ import with_statement
 
 # TO DO
 # handle fields that have a type but no name