When resolving outer fields, Item_field::fix_outer_fields()
creates new Item_refs for each execution of a prepared statement, so
these must be allocated in the runtime memroot. The memroot switching
before resolving JOIN::having causes these to be allocated in the
statement root, leaking memory for each PS execution.


sql/item_subselect.cc:
  addon, fix for 11829691, item could be created in
  runtime memroot, so we need to use real_item instead.