mysql-test/r/subselect.result:
  testst of IN subqueries with row
mysql-test/t/subselect.test:
  tests of ion subqueries with row
sql/item.h:
  add method to prevent of removing Item_ref_null_helper from HAVING
sql/item_cmpfunc.h:
  Prevented removing of Item_test_isnotnull from HAVING
sql/item_subselect.cc:
  fixed converting row IN subqueries
sql/sql_select.cc:
  fixed debug print