bpo-13153: Use OS native encoding for converting between Python and Tcl. (GH-16545)

On Windows use UTF-16 (or UTF-32 for 32-bit Tcl_UniChar) with the
"surrogatepass" error handler for converting to/from Tcl Unicode objects.

On Linux use UTF-8 with the "surrogateescape" error handler for converting
to/from Tcl String objects.

Converting strings from Tcl to Python and back now never fails
(except MemoryError).

Lib/idlelib/runscript.py

@@ -147,8 +147,7 @@ class ScriptBinding:
         interp = self.shell.interp
         if pyshell.use_subprocess and restart:
             interp.restart_subprocess(
-                    with_cwd=False, filename=
-                    self.editwin._filename_to_unicode(filename))
+                    with_cwd=False, filename=filename)
         dirname = os.path.dirname(filename)
         argv = [filename]
         if self.cli_args: