Issue #4471: Properly shutdown socket in IMAP.shutdown().  Patch by
Lorenzo M. Catucci.
diff --git a/Lib/test/test_imaplib.py b/Lib/test/test_imaplib.py
index 8d86ce6..351659d 100644
--- a/Lib/test/test_imaplib.py
+++ b/Lib/test/test_imaplib.py
@@ -217,6 +217,7 @@
 
     def test_logout(self):
         rs = self.server.logout()
+        self.server = None
         self.assertEqual(rs[0], 'BYE')