Fix another ResourceWarning in test_packaging.

Lib/packaging/tests/pypi_server.py

@@ -149,6 +149,7 @@ class PyPIServer(threading.Thread):
     def stop(self):
         """self shutdown is not supported for python < 2.6"""
         self._run = False
+        if self.is_alive():
             self.join()
         self.server.server_close()
 

Lib/packaging/tests/test_pypi_simple.py

@@ -233,6 +233,7 @@ class SimpleCrawlerTestCase(TempdirManager,
             self.assertEqual(4, len(crawler.get_releases("foo")))
         finally:
             mirror.stop()
+            server.stop()
 
     def test_simple_link_matcher(self):
         # Test that the simple link matcher finds the right links"""