title: Apostrophe in the title of feed generates error
body: <p>When I try to generate the feed and these contain the title <code>'</code> in the browser which is interpreted as <code>’</code> browsers generate an error right at the character <code>’</code>, MySql contains the <code>'</code> and not <code>’</code> i try to replace with php but not work.  </p>
  
  <pre><code>$domanda = mysqli_query($conn, "SELECT * FROM wp_posts WHERE post_status = 'publish' and post_type = 'post' AND DATE(post_modified) &gt; DATE(post_date) ORDER BY post_modified DESC LIMIT 50");
      $numrss = mysqli_num_rows($domanda);
      while ($info = $domanda-&gt;fetch_array(MYSQLI_ASSOC))
      {
      $primodato=$info['post_title'];
      echo "&lt;item&gt;
      &lt;title&gt;&lt;![CDATA[".str_replace("'"," ",$primodato)."]]&gt;&lt;/title&gt;";
  </code></pre>
  
  <p><a href="http://i.stack.imgur.com/aFAgQ.png" rel="nofollow">Browser</a></p>
  
  <p><a href="http://i.stack.imgur.com/z5Klh.png" rel="nofollow">MySql</a></p>
  
  <p>any solution?</p>
  
  <p>header is set correct (i think)</p>
  
  <pre><code>&lt;?php header("Content-type: text/xml; charset=utf-8");
  </code></pre>