Description:
------------
The setIteratorMode method seems to cut everything above 3 (IT_MODE_LIFO | IT_MODE_DELETE) to 0.

This is most unfortunate, because one can not define any user flags. For example I can't do anything of sort:

<?php
class MyList extends SplDoublyLinkedList
{
    const IT_MODE_PLUS_ONE = 512;

    public function current()
    {
        $val = parent::current();
        if ( 0 != $this->getIteratorMode() & self::IT_MODE_PLUS_ONE ) {
            return $val + 1;
        }
        return $val;
    }
}


$List = new MyList();
$List->setIteratorMode( $List->getIteratorMode() | MyList::IT_MODE_PLUS_ONE );
$List->push(5);
$List->push(6);

foreach ( $List as $value ) {
    echo "{$value}\n";
}
?>

Test script:
---------------
$Sl = new SplStack();

$Sl->setIteratorMode(3);
var_dump($Sl->getIteratorMode());

$Sl->setIteratorMode(4);
var_dump($Sl->getIteratorMode());

Expected result:
----------------
setIteratorMode should accept any provided integer

Actual result:
--------------
the mode is stripped down to 0 if provided integer is greater then 3