Change the PyUnit-based tests to use the test_main() approach.  This
allows using the tests with unittest.py as a script.  The tests will
still run when run as a script themselves.
diff --git a/Lib/test/test_mhlib.py b/Lib/test/test_mhlib.py
index 30f8ca3..9d5f101 100644
--- a/Lib/test/test_mhlib.py
+++ b/Lib/test/test_mhlib.py
@@ -331,4 +331,10 @@
         msg.fp.close()
         del msg
 
-run_unittest(MhlibTests)
+
+def test_main():
+    run_unittest(MhlibTests)
+
+
+if __name__ == "__main__":
+    test_main()