Description:
------------
The JSON serializer, as configured with

$memcached->setOption(Memcached::OPT_SERIALIZER, 
Memcached::SERIALIZER_JSON);

returns objects upon deserialization (i.e. $memcached-
>get(...)) even if an array was added in the first place.

It seems as though internally, json_decode($s) is being used 
instead of json_decode($s, true).

(Perhaps there needs to be an Memcached::SERIALIZER_JSON and 
Memcached::SERIALIZER_JSON_OBJECT serialization styles.)

Reproduce code:
---------------
$memcached = new Memcached();

$memcached->setOption(Memcached::OPT_SERIALIZER, Memcached::SERIALIZER_JSON);
$memcached->addServers(array(array("localhost", 11211)));
                             
$a1 = array("bar" => 3);

print_r($a1);

$memcached->set("foo", $a1);

$a2 = $memcached->get("foo");

print_r($a2);
 

Expected result:
----------------
Array
(
    [bar] => 3
)
Array
(
    [bar] => 3
)


Actual result:
--------------
Array
(
    [bar] => 3
)
stdClass Object
(
    [bar] => 3
)