mysql-test/r/subselect.result:
  cleaning up of results of subselects test
mysql-test/t/subselect.test:
  cleaning up of results of subselects test
sql/item_subselect.cc:
  call result object cleupup on engine cleunup
sql/sql_class.cc:
  added cleanup of select_max_min_finder_subselect
sql/sql_class.h:
  added cleanup of select_max_min_finder_subselect