<?php

echo "Animal.php\n";

class Animal extends Creature
{

}

<?php

echo "Animal.php\n";
require_once('Cat.php');

class Animal extends Creature
{

}

Revert "No fatal when not requiring Cat.php from Animal.php"
Revert "No fatal when not requiring Cat.php from Animal.php"

Re-introduce fatal error.

This reverts commit 9b1c11819d8b65ecfc81a787067b51ab6258e4ce.
