[ticket/13062] Add viewforum.php core event to modify topic ids sql query

Event request: http://area51.phpbb.com/phpBB/viewtopic.php?f=111&t=45383

PHPBB3-13062
Merge pull request #2949 from rxu/ticket/13062

[ticket/13062] Add viewforum.php core event to modify topic ids sql query

* rxu/ticket/13062:
  [ticket/13062] Add viewforum.php core event to modify topic ids sql query