title: Convert to/from date format
body: <p>I'm trying to convert to and from a <code>DateTime</code> using <code>z Y</code> format (day number/year) but it seems to be off by 1 day:</p>
  
  <pre><code>&lt;?php
  var_dump(DateTime::createFromFormat('z Y', '239 2016'));
  var_dump(DateTime::createFromFormat('d/m/Y', '28/08/2016'));
  var_dump(DateTime::createFromFormat('d/m/Y', '28/08/2016')-&gt;format('z Y'));
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>object(DateTime)#1 (3) {
    ["date"]=&gt;
    string(26) "2016-08-28 01:08:44.000000"
    ["timezone_type"]=&gt;
    int(3)
    ["timezone"]=&gt;
    string(16) "Europe/Amsterdam"
  }
  object(DateTime)#1 (3) {
    ["date"]=&gt;
    string(26) "2016-08-28 01:08:44.000000"
    ["timezone_type"]=&gt;
    int(3)
    ["timezone"]=&gt;
    string(16) "Europe/Amsterdam"
  }
  string(8) "240 2016"
  </code></pre>
  
  <p><a href="https://3v4l.org/p1rnL" rel="nofollow">https://3v4l.org/p1rnL</a></p>
  
  <p>Is this a bug, or am I doing something wrong?</p>
  
  <hr>
  
  <p>Using day 0/the 1st of Jan seems to work as expected: <a href="https://3v4l.org/BqIkM" rel="nofollow">https://3v4l.org/BqIkM</a></p>