Fix unix socket test on linux.

Unix socket addresses are bytes on linux (but str on mac).  This mostly
works but causes errors in py3's -bb strict mode.

maint/vm/ubuntu12.04/tox.ini

@@ -28,3 +28,7 @@ deps =
      pycurl
      twisted==12.2.0
 commands = python -m tornado.test.runtests --ioloop=tornado.platform.twisted.TwistedIOLoop {posargs:}
+
+[testenv:py32]
+basepython = python3.2
+commands = python -bb -m tornado.test.runtests {posargs:}

tornado/httpserver.py

@@ -30,6 +30,7 @@ from __future__ import absolute_import, division, print_function, with_statement
 
 import socket
 
+from tornado.escape import native_str
 from tornado.http1connection import HTTP1ServerConnection, HTTP1ConnectionParameters
 from tornado import gen
 from tornado import httputil
@@ -207,6 +208,11 @@ class _HTTPRequestContext(object):
     def __str__(self):
         if self.address_family in (socket.AF_INET, socket.AF_INET6):
             return self.remote_ip
+        elif isinstance(self.address, bytes):
+            # Python 3 with the -bb option warns about str(bytes),
+            # so convert it explicitly.
+            # Unix socket addresses are str on mac but bytes on linux.
+            return native_str(self.address)
         else:
             return str(self.address)