title: Wrong charset after re.sub()
body: <p>I have this code </p>
  
  <pre><code>import chardet, re    
  
  content = "Бланк свидетельства о допуске."
  print content
  print chardet.detect(content)
  content = re.sub(u"(?i)[^-0-9a-zа-яё«»\&amp;\;\/\&lt;\&gt;\.,\s\(\)\*:!\?]", "", content)
  print content
  print chardet.detect(content)
  </code></pre>
  
  <p>And output</p>
  
  <pre><code>Бланк свидетельства о допуске.
  {'confidence': 0.99, 'encoding': 'utf-8'}
  � �  .
  {'confidence': 0.5, 'encoding': 'windows-1252'}
  </code></pre>
  
  <p>What am I doing wrong? How can I get uft-8 string after <code>re.sub()</code>? 
  (Python 2.7,<code># coding: utf-8</code>, file in UTF-8, IDE Pycharm).</p>
  
  <p>Thanks.</p>