Make the it_index field in the str/unicode iterators Py_ssize_t's.
Test the new iterators on str/unicode.
diff --git a/Lib/test/test_str.py b/Lib/test/test_str.py
index 45942a6..226a168 100644
--- a/Lib/test/test_str.py
+++ b/Lib/test/test_str.py
@@ -19,6 +19,14 @@
         string_tests.MixinStrUnicodeUserStringTest.test_formatting(self)
         self.assertRaises(OverflowError, '%c'.__mod__, 0x1234)
 
+    def test_iterators(self):
+        # Make sure str objects have an __iter__ method
+        it = "abc".__iter__()
+        self.assertEqual(it.next(), "a")
+        self.assertEqual(it.next(), "b")
+        self.assertEqual(it.next(), "c")
+        self.assertRaises(StopIteration, it.next)
+
     def test_conversion(self):
         # Make sure __str__() behaves properly
         class Foo0: