title: Convert criteria to detached criteria
body: <p>This question is titled similar to <a href="https://stackoverflow.com/q/35424717/581205">this one</a>, but it's no duplicate as the other OP actually wanted something else (anyway, there's no answer to my question there). What I want is to recycle my already constructed <code>Criteria</code> in <code>Subqueries.exists(DetachedCriteria)</code>.</p>
  
  <p>I know that <code>Criteria</code> is basically <code>DetachedCriteria</code> with an attached <code>Session</code>, so I'd expect something like <code>Criteria#toDetached()</code> or a factory method on the other side, but I can't find anything.</p>