Description:
------------
Consider the code below:

it does not produce correct results on 4.4, 5.1 head, but worked in some 5.0 versions due to the fact that key() is defined as by-ref function in 5.0. 

Reproduce code:
---------------
<?
$state = array("one" => 1, "two" => 2, "three" => 3);
function foo( &$state ) {
    $contentDict = end( $state );
    for ( $contentDict = end( $state ); $contentDict !== false; $contentDict = prev( $state ) ) {
        echo key($state)."\n";
    }
}
foo($state);
?>


Expected result:
----------------
three two one

Actual result:
--------------
one one one