title: doctrine2 native query update statement
body: <p>How to do a native sql query in Doctrine 2, executing an update statement?
  The createNativeQuery method on EntityManager, requires a second parameter (ResultSetMapping) to be able to map the resultsets to Objects.</p>
  
  <p>But when updating (or inserting, or set, or...) there is no resulset to map.
  Passing null or just new ResultSetMapping(), gives an error.</p>
  
  <p>Are only select queries supported for native sql?</p>