Replace backticks with repr() or "%r"

From SF patch #852334.
diff --git a/Demo/sockets/radio.py b/Demo/sockets/radio.py
index 6131d40..b68a4ec 100755
--- a/Demo/sockets/radio.py
+++ b/Demo/sockets/radio.py
@@ -10,5 +10,5 @@
 
 while 1:
 	data, wherefrom = s.recvfrom(1500, 0)
-	sys.stderr.write(`wherefrom` + '\n')
+	sys.stderr.write(repr(wherefrom) + '\n')
 	sys.stdout.write(data)