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_collections.py b/Lib/test/test_collections.py
index f92eb6f..86b47de 100644
--- a/Lib/test/test_collections.py
+++ b/Lib/test/test_collections.py
@@ -91,7 +91,7 @@
 
     def test_Hashable(self):
         # Check some non-hashables
-        non_samples = [bytes(), list(), set(), dict()]
+        non_samples = [buffer(), list(), set(), dict()]
         for x in non_samples:
             self.failIf(isinstance(x, Hashable), repr(x))
             self.failIf(issubclass(type(x), Hashable), repr(type(x)))
@@ -100,7 +100,7 @@
                    int(), float(), complex(),
                    str(),
                    tuple(), frozenset(),
-                   int, list, object, type,
+                   int, list, object, type, bytes()
                    ]
         for x in samples:
             self.failUnless(isinstance(x, Hashable), repr(x))