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_descr.py b/Lib/test/test_descr.py
index 67ae239..961369f 100644
--- a/Lib/test/test_descr.py
+++ b/Lib/test/test_descr.py
@@ -3145,7 +3145,7 @@
 
     class octetstring(str):
         def __str__(self):
-            return str(binascii.b2a_hex(self))
+            return binascii.b2a_hex(self).decode("ascii")
         def __repr__(self):
             return self + " repr"