Change ILIKE to invoke lower() and then do plain LIKE comparison when

Change ILIKE to invoke lower() and then do plain LIKE comparison when
working in a multibyte encoding.  This fixes the problems exhibited in
bug #1931 and other reports of ILIKE misbehavior in UTF8 encoding.
It's a pretty grotty solution though --- should rethink how to do it
after we install better locale support, someday.