title: How do I revert back to a previous SVN commit?
body: <p>Suppose I'm at revision 50. 
  But, I want to revert back to revision 45, and commit back as the stable version.</p>
  
  <p>How do I do that, in the most simple way?</p>
  
  <ol>
  <li>What if I want to do that with one file?</li>
  <li>What if I want to do that with the entire repository?</li>
  </ol>