Replace backticks with repr() or "%r"

From SF patch #852334.
diff --git a/Demo/sockets/broadcast.py b/Demo/sockets/broadcast.py
index a02b081..010162c 100755
--- a/Demo/sockets/broadcast.py
+++ b/Demo/sockets/broadcast.py
@@ -10,7 +10,7 @@
 s.setsockopt(SOL_SOCKET, SO_BROADCAST, 1)
 
 while 1:
-	data = `time.time()` + '\n'
+	data = repr(time.time()) + '\n'
 	s.sendto(data, ('<broadcast>', MYPORT))
 	time.sleep(2)