Add renaming notices to thread and dummy_thread.

Doc/library/dummy_thread.rst

-
 :mod:`dummy_thread` --- Drop-in replacement for the :mod:`thread` module
 ========================================================================
 
 .. module:: dummy_thread
    :synopsis: Drop-in replacement for the thread module.
 
+.. note::
+   The :mod:`dummy_thread` module has been renamed to :mod:`_dummy_thread` in
+   Python 3.0.  The :term:`2to3` tool will automatically adapt imports when
+   converting your sources to 3.0; however, you should consider using the
+   high-lever :mod:`dummy_threading` module instead.
+
 
 This module provides a duplicate interface to the :mod:`thread` module.  It is
 meant to be imported when the :mod:`thread` module is not provided on a

Doc/library/thread.rst

-
 :mod:`thread` --- Multiple threads of control
 =============================================
 
 .. module:: thread
    :synopsis: Create multiple threads of control within one interpreter.
 
+.. note::
+   The :mod:`thread` module has been renamed to :mod:`_thread` in Python 3.0.
+   The :term:`2to3` tool will automatically adapt imports when converting your
+   sources to 3.0; however, you should consider using the high-lever
+   :mod:`threading` module instead.
+
 
 .. index::
    single: light-weight processes