[ticket/12758] Add show_results var to core.search_modify_rowset

PHPBB3-12758
[ticket/12758] Add @changed to doc block

PHPBB3-12758
Merge pull request #2635 from PayBas/ticket/12758

[ticket/12758] Add show_results var to core.search_modify_rowset

* PayBas/ticket/12758:
  [ticket/12758] Add @changed to doc block
  [ticket/12758] Add show_results var to core.search_modify_rowset