f one
  wants to do further operations (such as <code>update</code>) on the fitted
  model.  However, the refitted model will still be slightly different
  from the equivalent model fitted via <code>update</code>; in particular, the
  <code>terms</code> component is not updated to reflect the new response
  variable, if it has a different name from the original.</p>
<p>If <code>newresp</code> has an <code>na.action</code> attribute, then it is
  assumed that NA values have already been removed from the nume