I re-encoded CREDITS to utf-8 and specified 'ascii' for the other so *I* will see an error if a non-ascii chars gets in the file again.  Serhiy, I am confident that this will work on all OSes, but feel free to test AboutIDLE again sometime.

(Note to myself) To automate a test that the files will open, change
from idlelib import textView  # to
from idlelib.textView import view_text, view_file
and change display... and show.. methods to module functions so view_file can be replaced and the show functions called without involving tkinter.  This can be part of future refactoring in 3.5+.