bug 4521: unique key prefix interacts poorly with utf8: fixed length key fix.


myisam/mi_key.c:
  bug 4521: unique key prefix interacts poorly with utf8: fixed length key fix.
mysql-test/t/ctype_utf8.test:
  bug 4521: unique key prefix interacts poorly with utf8: fixed length key fix.
mysql-test/r/ctype_utf8.result:
  bug 4521: unique key prefix interacts poorly with utf8: fixed length key fix.