Try to prevent hangs on Tru64/Alpha buildbot. I'm not certain this will help

and may need to be reverted if it causes problems.

Lib/test/test_signal.py

@@ -43,7 +43,8 @@ def handlerB(*args):
         print "handlerB", args
     raise HandlerBCalled, args
 
-signal.alarm(20)                        # Entire test lasts at most 20 sec.
+MAX_DURATION = 20
+signal.alarm(MAX_DURATION)   # Entire test should last at most 20 sec.
 hup = signal.signal(signal.SIGHUP, handlerA)
 usr1 = signal.signal(signal.SIGUSR1, handlerB)
 usr2 = signal.signal(signal.SIGUSR2, signal.SIG_IGN)
@@ -71,9 +72,34 @@ try:
 except TypeError:
     pass
 
+# Set up a child to send an alarm signal to us (the parent) after waiting
+# long enough to receive the alarm.  It seems we miss the alarm for some
+# reason.  This will hopefully stop the hangs on Tru64/Alpha.
+def force_test_exit():
+    # Sigh, both imports seem necessary to avoid errors.
+    import os
+    fork_pid = os.fork()
+    if fork_pid == 0:
+        # In child
+        import os, time
+        try:
+            # Wait 5 seconds longer than the expected alarm to give enough
+            # time for the normal sequence of events to occur.  This is
+            # just a stop-gap to prevent the test from hanging.
+            time.sleep(MAX_DURATION + 5)
+            for i in range(3):
+                os.kill(pid, signal.SIGALARM)
+        finally:
+            os._exit(0)
+    # In parent (or error)
+    return fork_pid
+
 try:
     os.system(script)
 
+    # Try to ensure this test exits even if there is some problem with alarm.
+    # Tru64/Alpha sometimes hangs and is ultimately killed by the buildbot.
+    fork_pid = force_test_exit()
     print "starting pause() loop..."
 
     try:
@@ -94,6 +120,16 @@ try:
         if verbose:
             print "KeyboardInterrupt (assume the alarm() went off)"
 
+    # Forcibly kill the child we created to ping us if there was a test error.
+    try:
+        # Make sure we don't kill ourself if there was a fork error.
+        if fork_pid > 0:
+            os.kill(fork_pid, signal.SIGKILL)
+    except:
+        # If the child killed us, it has probably exited.  Killing a
+        # non-existant process will raise an error which we don't care about.
+        pass
+
     if not a_called:
         print 'HandlerA not called'