Switch wsgiref to io.{StringIO,BytesIO}.  This shuts up the test failures.
(I'm not sure about it actually working though.)
diff --git a/Lib/test/test_wsgiref.py b/Lib/test/test_wsgiref.py
index 213c5cf..544e42b 100755
--- a/Lib/test/test_wsgiref.py
+++ b/Lib/test/test_wsgiref.py
@@ -7,7 +7,7 @@
 from wsgiref.validate import validator
 from wsgiref.simple_server import WSGIServer, WSGIRequestHandler, demo_app
 from wsgiref.simple_server import make_server
-from StringIO import StringIO
+from io import StringIO, BytesIO
 from SocketServer import BaseServer
 import re, sys
 
@@ -47,9 +47,9 @@
     ])
     return ["Hello, world!"]
 
-def run_amock(app=hello_app, data="GET / HTTP/1.0\n\n"):
+def run_amock(app=hello_app, data=b"GET / HTTP/1.0\n\n"):
     server = make_server("", 80, app, MockServer, MockHandler)
-    inp, out, err, olderr = StringIO(data), StringIO(), StringIO(), sys.stderr
+    inp, out, err, olderr = BytesIO(data), StringIO(), StringIO(), sys.stderr
     sys.stderr = err
 
     try: