bug#7833:  Wrong datatype of aggregate column is returned


mysql-test/r/func_group.result:
  Test case for bug 7833:  Wrong datatype of aggregate column is returned
mysql-test/r/union.result:
  Test case for bug 6931: Date Type column problem when using UNION-Table.
mysql-test/t/func_group.test:
  Test case for bug 7833:  Wrong datatype of aggregate column is returned
mysql-test/t/union.test:
  Test case for bug 6931: Date Type column problem when using UNION-Table.