fix syntax of xtest_signal.py on python2.6

greentest/xtest_signal.py

@@ -38,7 +38,8 @@ def test_main():
     # re-raises information about any exceptions the child
     # throws. The real work happens in self.run_test().
     os_done_r, os_done_w = os.pipe()
-    with closing(os.fdopen(os_done_r)) as done_r, closing(os.fdopen(os_done_w, 'w')) as done_w:
+    with closing(os.fdopen(os_done_r)) as done_r:
+        with closing(os.fdopen(os_done_w, 'w')) as done_w:
             child = gevent.fork()
             if not child:
                 # In the child process; run the test and report results