[Mediawiki-l] How to return HTTP 404 for a non-existent page?

[Javier Valcarce García]

Some time ago, I ask this same question, the solution, given to me by
Platonides, was to change a line in the source code of MediaWiki 1.10

if ( 0 == $this->getID() ) {
    wfProfileOut( __METHOD__ );
    $wgOut->setStatusCode(404); // CHANGED


Now, I have MediaWiki 1.12, What are the lines I must change now? Why
not include permanently this feature in the main source code?