Fix for issue3559: No preferences menu in IDLE on OSX

1) Add a comment to the help file to that points to the
   preferences menu.

2) An earlier checkin tried to detect Tk >= 8.10.14,
   but did this in the wrong way. The end result of this
   was that the IDLE->Preferences... menu got surpressed
   when using the system version of Tcl/Tk
diff --git a/Lib/idlelib/macosxSupport.py b/Lib/idlelib/macosxSupport.py
index 222abfc..279b1cc 100644
--- a/Lib/idlelib/macosxSupport.py
+++ b/Lib/idlelib/macosxSupport.py
@@ -89,7 +89,9 @@
 
     ###check if Tk version >= 8.4.14; if so, use hard-coded showprefs binding
     tkversion = root.tk.eval('info patchlevel')
-    if tkversion >= '8.4.14':
+    # Note: we cannot check if the string tkversion >= '8.4.14', because
+    # the string '8.4.7' is greater than the string '8.4.14'.
+    if map(int, tkversion.split('.')) >= (8, 4, 14):
         Bindings.menudefs[0] =  ('application', [
                 ('About IDLE', '<<about-idle>>'),
                 None,