Merging the py3k-pep3137 branch back into the py3k branch.
No detailed change log; just check out the change log for the py3k-pep3137
branch.  The most obvious changes:

  - str8 renamed to bytes (PyString at the C level);
  - bytes renamed to buffer (PyBytes at the C level);
  - PyString and PyUnicode are no longer compatible.

I.e. we now have an immutable bytes type and a mutable bytes type.

The behavior of PyString was modified quite a bit, to make it more
bytes-like.  Some changes are still on the to-do list.
diff --git a/Lib/test/test_urllib2.py b/Lib/test/test_urllib2.py
index 5cbc652..393e997 100644
--- a/Lib/test/test_urllib2.py
+++ b/Lib/test/test_urllib2.py
@@ -999,7 +999,8 @@
         self.assertEqual(len(http_handler.requests), 2)
         self.assertFalse(http_handler.requests[0].has_header(auth_header))
         userpass = bytes('%s:%s' % (user, password), "ascii")
-        auth_hdr_value = 'Basic ' + str(base64.encodestring(userpass)).strip()
+        auth_hdr_value = ('Basic ' +
+            base64.encodestring(userpass).strip().decode())
         self.assertEqual(http_handler.requests[1].get_header(auth_header),
                          auth_hdr_value)