Instructs the system to temporarily ignore a given key/target.
At times we need to temporarily disable slave queries. To do so, call this method with the database key and the target to disable. That database key will then always fall back to 'default' for that key, even if it's defined.
$key: The database connection key.
$target: The target of the specified key to ignore.
public static function ignoreTarget($key, $target) {
self::$ignoreTargets[$key][$target] = TRUE;
}