This bug manifested itself for join queries with GROUP BY and HAVING clauses
whose SELECT lists contained DISTINCT. It occurred when the optimizer could
deduce that the result set would have not more than one row.
The bug could lead to wrong result sets for queries of this type because
HAVING conditions were erroneously ignored in some cases in the function
remove_duplicates.   


mysql-test/r/having.result:
  Added a test case for bug #29911.
mysql-test/t/having.test:
  Added a test case for bug #29911.