Problem: ENUM columns are sorted and distributed according to their
numeric value, but Field::hash() incorrectly passed string character set
(utf32) in combination with numeric value to the hash function,
which made assertion fail.

Fix: pass "binary" character set in combination with numeric value
to the hash function.

  mysql-test/suite/parts/r/part_ctype_utf32.result
  Adding tests

  mysql-test/suite/parts/t/part_ctype_utf32.test
  Adding test

  sql/field.cc
  Pass correct character set pointer to the hash function.