Revised the test suite for 'contains' to use the test() function argument
rather than vereq().  While it was effectively testing regular strings, it
ignored the test() function argument when called by test_userstring.py.
diff --git a/Lib/test/string_tests.py b/Lib/test/string_tests.py
index c8feb19..1729999 100644
--- a/Lib/test/string_tests.py
+++ b/Lib/test/string_tests.py
@@ -305,12 +305,12 @@
         raise TestFailed, msg
 
 def run_contains_tests(test):
-    vereq('' in '', True)
-    vereq('' in 'abc', True)
-    vereq('\0' in 'abc', False)
-    vereq('\0' in '\0abc', True)
-    vereq('\0' in 'abc\0', True)
-    vereq('a' in '\0abc', True)
-    vereq('asdf' in 'asdf', True)
-    vereq('asdf' in 'asd', False)
-    vereq('asdf' in '', False)
+    test('__contains__', '', True, '')         # vereq('' in '', True)
+    test('__contains__', 'abc', True, '')      # vereq('' in 'abc', True)
+    test('__contains__', 'abc', False, '\0')   # vereq('\0' in 'abc', False)
+    test('__contains__', '\0abc', True, '\0')  # vereq('\0' in '\0abc', True)
+    test('__contains__', 'abc\0', True, '\0')  # vereq('\0' in 'abc\0', True)
+    test('__contains__', '\0abc', True, 'a')   # vereq('a' in '\0abc', True)
+    test('__contains__', 'asdf', True, 'asdf') # vereq('asdf' in 'asdf', True)
+    test('__contains__', 'asd', False, 'asdf') # vereq('asdf' in 'asd', False)
+    test('__contains__', '', False, 'asdf')    # vereq('asdf' in '', False)