Replace backticks with repr() or "%r"

From SF patch #852334.
diff --git a/Lib/idlelib/ScriptBinding.py b/Lib/idlelib/ScriptBinding.py
index c0fa88f..a1d937b 100644
--- a/Lib/idlelib/ScriptBinding.py
+++ b/Lib/idlelib/ScriptBinding.py
@@ -145,16 +145,16 @@
         dirname = os.path.dirname(filename)
         # XXX Too often this discards arguments the user just set...
         interp.runcommand("""if 1:
-            _filename = %s
+            _filename = %r
             import sys as _sys
             from os.path import basename as _basename
             if (not _sys.argv or
                 _basename(_sys.argv[0]) != _basename(_filename)):
                 _sys.argv = [_filename]
             import os as _os
-            _os.chdir(%s)
+            _os.chdir(%r)
             del _filename, _sys, _basename, _os
-            \n""" % (`filename`, `dirname`))
+            \n""" % (filename, dirname))
         interp.prepend_syspath(filename)
         interp.runcode(code)