Make test_warnings play nice with regrtest -R:: now that regrtest doesn't

always reload the module (specifically, it doesn't reload if the module has
a 'test_main'.)

Lib/test/test_warnings.py

@@ -82,11 +82,11 @@ class TestModule(unittest.TestCase):
         self.assertEqual(msg.category, 'UserWarning')
 
 def test_main(verbose=None):
-    test_support.run_unittest(TestModule)
-
-# Obscure hack so that this test passes after reloads (regrtest -R).
+    # Obscure hack so that this test passes after reloads or repeated calls
+    # to test_main (regrtest -R).
     if '__warningregistry__' in globals():
         del globals()['__warningregistry__']
+    test_support.run_unittest(TestModule)
 
 if __name__ == "__main__":
     test_main(verbose=True)