Description:
------------
When the binary protocol is enabled and when passing the 3rd 
parameter, Memcached::GET_PRESERVE_ORDER, to getMulti(), the 
resulting array contains non-unique keys.

In other words, each key is represented twice in the result. 
One is set to null and the other is set to the value of 
whatever was stored in memcached.

getResultMessage() shows "SUCCESS".

I'm actually on php 5.3.8

Reproduce code:
---------------
$MC = new Memcached;
$MC->setOption(Memcached::OPT_BINARY_PROTOCOL, true); // Removing this causes the code to work, but at the 'expense' of reverting to the ASCII protocol
$MC->addServer('localhost', 11211);

$KeyList = Array (
     'key1'
    ,'key2'
    ,'key3'
    ,'key4'
);

$Test = Array();
foreach ($KeyList as $k) {
    $Test[$k] = 'stored value for '.$k;
}

// This block uses the *Multi() functions
$MC->setMulti($Test, 3600);

sleep(1);
$null = null;
$theList = $MC->getMulti($KeyList, $null, Memcached::GET_PRESERVE_ORDER);

var_dump($theList);

Expected result:
----------------
var_dump should shows:

array
     'key1' => 'stored value for key1'
     'key2' => 'stored value for key2'
     'key3' => 'stored value for key3'
     'key4' => 'stored value for key4'

Actual result:
--------------
var_dump shows:

array
     'key1' => null
     'key2' => null
     'key3' => null
     'key4' => null
     'key1' => 'stored value for key1'
     'key2' => 'stored value for key2'
     'key3' => 'stored value for key3'
     'key4' => 'stored value for key4'