mysql-test/r/subselect.result:
  new test results
  test of bug 185
mysql-test/t/subselect.test:
  test of bug 185
sql/item.h:
  new method
sql/item_cmpfunc.cc:
  new Item to control NULL value in HAVING clouse
sql/item_cmpfunc.h:
  new Item to control NULL value in HAVING clouse
sql/item_subselect.cc:
  if IN was rewrited through WHERE thien it will be rewrited in following way:
  
  WHERE left_expr=item or is null(item) heving is_not_null_test(item)
sql/item_subselect.h:
  Item_is_not_null_test can change was_null flag
sql/sql_select.cc:
  some layout fix