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/_abcoll.py b/Lib/_abcoll.py
index 8f630bf..ec3e2f8 100644
--- a/Lib/_abcoll.py
+++ b/Lib/_abcoll.py
@@ -489,7 +489,7 @@
 
 Sequence.register(tuple)
 Sequence.register(str)
-Sequence.register(str8)
+Sequence.register(bytes)
 Sequence.register(memoryview)