SF patch# 1764815 by Paul Colomiets.
Fix for test_socketserver.
Use io.BytesIO instead of io.StringIO, and adjust tests.
diff --git a/Lib/SocketServer.py b/Lib/SocketServer.py
index c6e71eb..994a3c6 100644
--- a/Lib/SocketServer.py
+++ b/Lib/SocketServer.py
@@ -574,10 +574,10 @@
     """Define self.rfile and self.wfile for datagram sockets."""
 
     def setup(self):
-        from io import StringIO
+        from io import BytesIO
         self.packet, self.socket = self.request
-        self.rfile = StringIO(self.packet)
-        self.wfile = StringIO()
+        self.rfile = BytesIO(self.packet)
+        self.wfile = BytesIO()
 
     def finish(self):
         self.socket.sendto(self.wfile.getvalue(), self.client_address)