Replace backticks with repr() or "%r"

From SF patch #852334.
diff --git a/Lib/idlelib/textView.py b/Lib/idlelib/textView.py
index be3ade0..917a6cc 100644
--- a/Lib/idlelib/textView.py
+++ b/Lib/idlelib/textView.py
@@ -46,7 +46,7 @@
             textFile = open(fileName, 'r')
         except IOError:
             tkMessageBox.showerror(title='File Load Error',
-                    message='Unable to load file '+`fileName`+' .')
+                    message='Unable to load file %r .' % (fileName,))
         else:
             self.textView.insert(0.0,textFile.read())