Replace backticks with repr() or "%r"

From SF patch #852334.
diff --git a/Lib/test/test_socketserver.py b/Lib/test/test_socketserver.py
index 36396da..cee5593 100644
--- a/Lib/test/test_socketserver.py
+++ b/Lib/test/test_socketserver.py
@@ -43,7 +43,7 @@
     if sock in r:
         return sock.recv(n)
     else:
-        raise RuntimeError, "timed out on %s" % `sock`
+        raise RuntimeError, "timed out on %r" % (sock,)
 
 def testdgram(proto, addr):
     s = socket.socket(proto, socket.SOCK_DGRAM)