Description:
------------
Hello,
  I think I found a bug in array_multisort, when trying to sort a multi-dimensional array, which has string keys containing only digits.
On the resulting array, those keys are suppressed, and replaced by '0' for the first one, '1' for the second...

I had this error on PHP version 5.3.6, and on the last PHP 5.4 Snap revision: 322462, downloaded from php.net (tested with no .ini file)

Test script:
---------------
$t = array(
    'AZE' => array('SORT' => 'order #2', 'FOO' => 'xx'),
    '123' => array('SORT' => 'order #3', 'FOO' => 'xx'),
    'RTY' => array('SORT' => 'order #5', 'FOO' => 'xx'),
    '654' => array('SORT' => 'order #1', 'FOO' => 'xx'),
    'UIO' => array('SORT' => 'order #4', 'FOO' => 'xx'),
);
$W_ORDER = array();
foreach($t as $key => $row)
    $W_ORDER[(string)$key] = $row['SORT'];

array_multisort(
    $W_ORDER, SORT_ASC, SORT_STRING,
    $t
);
print_r($t);

Expected result:
----------------
Array
(
    [654] => Array
        (
            [SORT] => order #1
            [FOO] => xx
        )

    [AZE] => Array
        (
            [SORT] => order #2
            [FOO] => xx
        )

    [123] => Array
        (
            [SORT] => order #3
            [FOO] => xx
        )

    [UIO] => Array
        (
            [SORT] => order #4
            [FOO] => xx
        )

    [RTY] => Array
        (
            [SORT] => order #5
            [FOO] => xx
        )
)

Actual result:
--------------
Array
(
    [0] => Array
        (
            [SORT] => order #1
            [FOO] => xx
        )

    [AZE] => Array
        (
            [SORT] => order #2
            [FOO] => xx
        )

    [1] => Array
        (
            [SORT] => order #3
            [FOO] => xx
        )

    [UIO] => Array
        (
            [SORT] => order #4
            [FOO] => xx
        )

    [RTY] => Array
        (
            [SORT] => order #5
            [FOO] => xx
        )
)