Combine the functionality of test_support.run_unittest()
and test_support.run_classtests() into run_unittest()
and use it wherever possible.

Also don't use "from test.test_support import ...", but
"from test import test_support" in a few spots.

From SF patch #662807.
diff --git a/Lib/test/test_userdict.py b/Lib/test/test_userdict.py
index cbd3bd1..bcf60a5 100644
--- a/Lib/test/test_userdict.py
+++ b/Lib/test/test_userdict.py
@@ -395,11 +395,11 @@
         self.assertEqual(s, t)
 
 def test_main():
-    suite = unittest.TestSuite()
-    suite.addTest(unittest.makeSuite(TestMappingProtocol))
-    suite.addTest(unittest.makeSuite(UserDictTest))
-    suite.addTest(unittest.makeSuite(UserDictMixinTest))
-    test.test_support.run_suite(suite)
+    test.test_support.run_unittest(
+        TestMappingProtocol,
+        UserDictTest,
+        UserDictMixinTest
+    )
 
 if __name__ == "__main__":
     test_main()