Document the auth module's lack of python3 support

tornado/auth.py

@@ -43,6 +43,9 @@ Example usage for Google OpenID::
                 raise tornado.web.HTTPError(500, "Google auth failed")
             # Save the user with, e.g., set_secure_cookie()
 
+.. note::
+
+   The ``tornado.auth`` module is not yet compatible with Python 3.
 """
 
 import base64

website/templates/index.html

@@ -55,7 +55,7 @@ sudo python setup.py install</code></pre>
   <ul>
     <li>On Python 2.6 and 2.7, there are no dependencies outside the Python standard library, although <a href="http://pycurl.sourceforge.net/">PycURL</a> (version 7.18.2 or higher required; version 7.21.1 or higher recommended) may be used if desired.</li>
     <li>On Python 2.5, PycURL is required, along with <a href="http://pypi.python.org/pypi/simplejson/">simplejson</a> and the Python development headers (typically obtained by installing a package named something like <code>python-dev</code> from your operating system).</li>
-    <li>On Python 3.2, the <a href="http://pypi.python.org/pypi/distribute">distribute</a> package is required.</li>
+    <li>On Python 3.2, the <a href="http://pypi.python.org/pypi/distribute">distribute</a> package is required.  Note that Python 3 support is new and may have bugs; in particular the <code>tornado.auth</code> module is known not to work on Python 3.</li>
   </ul></p>
 
   <p><b>Platforms:</b> Tornado should run on any Unix-like platform, although