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/tempfile.py

@@ -497,7 +497,7 @@ class SpooledTemporaryFile:
         else:
             # Setting newline="\n" avoids newline translation;
             # this is important because otherwise on Windows we'd
-            # get double newline translation upon rollover().
+            # hget double newline translation upon rollover().
             self._file = _io.StringIO(encoding=encoding, newline="\n")
         self._max_size = max_size
         self._rolled = False