Replace backticks with repr() or "%r"

From SF patch #852334.
diff --git a/Mac/Demo/waste/wed.py b/Mac/Demo/waste/wed.py
index 7161ae5..5d84b40 100644
--- a/Mac/Demo/waste/wed.py
+++ b/Mac/Demo/waste/wed.py
@@ -338,7 +338,7 @@
 				data = fp.read()
 				fp.close()
 			except IOError, arg:
-				EasyDialogs.Message("IOERROR: "+`arg`)
+				EasyDialogs.Message("IOERROR: %r" % (arg,))
 				return
 		else:
 			path = None