Logically one might think that chr(128) would collate before chr(255) except
this is a case-insensitive comparison and internally we toupper() both args.
toupper(chr(128)) is 128. There is no upper-case equivalent of this char.
toupper(chr(255)) is 120 so chr(255) collates before chr(128) in this
case-insensitive comparison. And these are rather bogus characters to feed
to a natsort test anyway.
