Description:
------------
Fatal error:  Key element cannot be a reference



Reproduce code:
---------------
foreach($list as &$key=>&$value) {
    $key = $key+1;
    $value = $value+1;
}

This code will generate error:

    Fatal error:  Key element cannot be a reference



Expected result:
----------------
$list = array(1 => 2, 5 => 6);
foreach($list as &$key=>&$value) {
    $key = $key+1;
    $value = $value+1;
}


Expected result:

$list == array (
                2 => 3,
                6 => 7
               )

Actual result:
--------------
Fatal error:  Key element cannot be a reference