php BUG

``` php
$data = array(
    "flags" => array(
        0 => 16777216,
        2 => 4
    )
);

$data['flags'][1] = 65536;

var_dump(msgpack_unpack(msgpack_pack($data)) == $data);
```

keys became random. also happens if there are arrays like `array('ley' => 2, 2 => 1, 1 => 3)`
