[ticket/13047] Add $post_list array to core.viewtopic_modify_page_title event

PHPBB3-13047
Merge pull request #2929 from rxu/ticket/13047

[ticket/13047] Add $post_list array to core.viewtopic_modify_page_title event

* rxu/ticket/13047:
  [ticket/13047] Add $post_list array to core.viewtopic_modify_page_title event