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_weakref.py b/Lib/test/test_weakref.py
index b078b17..eb87720 100644
--- a/Lib/test/test_weakref.py
+++ b/Lib/test/test_weakref.py
@@ -534,12 +534,12 @@
         return self.__ref.copy()
 
 def test_main():
-    suite = unittest.TestSuite()
-    suite.addTest(unittest.makeSuite(ReferencesTestCase))
-    suite.addTest(unittest.makeSuite(MappingTestCase))
-    suite.addTest(unittest.makeSuite(WeakValueDictionaryTestCase))
-    suite.addTest(unittest.makeSuite(WeakKeyDictionaryTestCase))
-    test_support.run_suite(suite)
+    test_support.run_unittest(
+        ReferencesTestCase,
+        MappingTestCase,
+        WeakValueDictionaryTestCase,
+        WeakKeyDictionaryTestCase
+    )
 
 
 if __name__ == "__main__":