A subquery transformation changes the HAVING clause of the embedding query if the subquery contains
a GROUP BY clause. Yet the split_sum_func2 function was not applied to the modified HAVING clause.
This could result in wrong answers.


mysql-test/r/subselect.result:
  Added a test case for bug #16603.
mysql-test/t/subselect.test:
  Added a test case for bug #16603.