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_float.py b/Lib/test/test_float.py
index 4360c54..ca5e537 100644
--- a/Lib/test/test_float.py
+++ b/Lib/test/test_float.py
@@ -40,14 +40,14 @@
                           'chicken', 'unknown')
 
 BE_DOUBLE_INF = b'\x7f\xf0\x00\x00\x00\x00\x00\x00'
-LE_DOUBLE_INF = bytes(reversed(BE_DOUBLE_INF))
+LE_DOUBLE_INF = bytes(reversed(buffer(BE_DOUBLE_INF)))
 BE_DOUBLE_NAN = b'\x7f\xf8\x00\x00\x00\x00\x00\x00'
-LE_DOUBLE_NAN = bytes(reversed(BE_DOUBLE_NAN))
+LE_DOUBLE_NAN = bytes(reversed(buffer(BE_DOUBLE_NAN)))
 
 BE_FLOAT_INF = b'\x7f\x80\x00\x00'
-LE_FLOAT_INF = bytes(reversed(BE_FLOAT_INF))
+LE_FLOAT_INF = bytes(reversed(buffer(BE_FLOAT_INF)))
 BE_FLOAT_NAN = b'\x7f\xc0\x00\x00'
-LE_FLOAT_NAN = bytes(reversed(BE_FLOAT_NAN))
+LE_FLOAT_NAN = bytes(reversed(buffer(BE_FLOAT_NAN)))
 
 # on non-IEEE platforms, attempting to unpack a bit pattern
 # representing an infinity or a NaN should raise an exception.