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.

Lib/idlelib/OutputWindow.py

@@ -35,7 +35,7 @@ class OutputWindow(EditorWindow):
     # Act as output file
 
     def write(self, s, tags=(), mark="insert"):
-        if isinstance(s, (bytes, str8)):
+        if isinstance(s, (bytes, bytes)):
             s = s.decode(IOBinding.encoding, "replace")
         self.text.insert(mark, s, tags)
         self.text.see(mark)