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<?php
//add to functions.php
function no_self_ping( &$links ) {
	$home = get_option( 'home' );
	foreach ( $links as $l => $link )
		if ( 0 === strpos( $link, $home ) )
			unset($links[$l]);
}

add_action( 'pre_ping', 'no_self_ping' );
?>