title: Memcached::getMulti() returning an empty array
body: <p>Tried using <code>Memcached::getMulti()</code> instead of fetching one cache key at a time.
  The result was an empty array(). I used the debugger to ensure that I was passing an indexed array of keys and I made sure the keys were in cache. Why is memcached returning an empty array when I know for sure the keys exist?</p>
  
  <pre><code>$mc-&gt;get('MYKEY');
  </code></pre>
  
  <p>vs.</p>
  
  <pre><code>$mc-&gt;getMulti(array([0]=&gt;'MYKEY0',[1]=&gt;'MYKEY1',[2]=&gt;'MYKEY2'));
  </code></pre>