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
3 files changed