Add future import to fix tests on 2.5

diff --git a/tornado/test/stack_context_test.py b/tornado/test/stack_context_test.py
index 1a1e9150282401cb625964ffde33e07673ff271c..4237d344824911641a8dd1d5e6d7d5d6f5de7998 100755 (executable)
--- a/tornado/test/stack_context_test.py
+++ b/tornado/test/stack_context_test.py
@@ -1,4 +1,5 @@
 #!/usr/bin/env python
+from __future__ import with_statement
 
 from tornado.stack_context import StackContext, wrap
 from tornado.testing import AsyncHTTPTestCase, AsyncTestCase, LogTrapTestCase