Change key binding to avoid conflict.

Lib/idlelib/config-keys.def

@@ -113,8 +113,8 @@ do-nothing=<Control-Key-F12>
 end-of-file=<Control-Key-d>
 python-docs=<Key-F1>
 python-context-help=<Shift-Key-F1> 
-history-next=<Command-Key-n>
-history-previous=<Shift-Command-Key-n>
+history-next=<Control-Key-n>
+history-previous=<Control-Key-p>
 interrupt-execution=<Control-Key-c>
 open-class-browser=<Command-Key-b>
 open-module=<Command-Key-m>