fix test_socket.py: to use hub's signal method if available (for libevent hub)

greentest/test_socket.py

@@ -888,6 +888,10 @@ class TCPTimeoutTest(SocketTCPTest):
             pass
         def alarm_handler(signal, frame):
             raise Alarm
+        from eventlet.api import get_hub
+        if hasattr(get_hub(), 'signal'):
+            myalarm = get_hub().signal(signal.SIGALRM, alarm_handler)
+        else:
             old_alarm = signal.signal(signal.SIGALRM, alarm_handler)
         try:
             try:
@@ -907,6 +911,9 @@ class TCPTimeoutTest(SocketTCPTest):
                 self.fail("got Alarm in wrong place")
         finally:
             # no alarm can be pending.  Safe to restore old handler.
+            if hasattr(get_hub(), 'signal'):
+                myalarm.cancel()
+            else:
                 signal.signal(signal.SIGALRM, old_alarm)
 
 class UDPTimeoutTest(SocketUDPTest):