title: Why SplPriorityQueue keys are reversed?
body: <p>The following code:</p>
  
  <pre><code>$queue = new \SplPriorityQueue();
  $queue-&gt;insert('a', 4);
  $queue-&gt;insert('b', 3);
  $queue-&gt;insert('d', 1);
  $queue-&gt;insert('c', 2);
  foreach($queue as $key =&gt; $value) {
    print "$key:$value\n";
  }
  </code></pre>
  
  <p>Outputs:</p>
  
  <pre><code>3:a 
  2:b 
  1:c 
  0:d
  </code></pre>
  
  <p>Expected behavior:</p>
  
  <pre><code>0:a 
  1:b 
  2:c 
  3:d
  </code></pre>
  
  <p>Is it bug or am I missing something?</p>