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IDLE is intended to present a simple interface to
beginners and to encourage good style.  I believe that
GvR made a deliberate decision not to have a horiz
scroll bar to discourage lines longer that 80 char.

If you want to code a patch,  I'd accept it.  However,
the config switch should be in config-main.def only, and
the selection should not appear on the Options dialog.

That way an experienced user could set it in
.idlerc/config-main.cfg