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/Modules/sha1module.c b/Modules/sha1module.c
index d96fe35..6ba03ad 100644
--- a/Modules/sha1module.c
+++ b/Modules/sha1module.c
@@ -339,7 +339,7 @@
 
     temp = self->hash_state;
     sha1_done(&temp, digest);
-    return PyBytes_FromStringAndSize((const char *)digest, SHA1_DIGESTSIZE);
+    return PyString_FromStringAndSize((const char *)digest, SHA1_DIGESTSIZE);
 }
 
 PyDoc_STRVAR(SHA1_hexdigest__doc__,