make the code compatible with python2.4

gevent/pool.py

@@ -91,6 +91,7 @@ class GreenletSet(object):
 
     def kill(self, exception=GreenletExit, block=True, timeout=None):
         timer = Timeout.start_new(timeout)
+        try:
             try:
                 while self.greenlets:
                     for greenlet in list(self.greenlets):