Update an existing {@link Prediction}.
<P>The outcome date is set only when the outcome itself has changed from its previous value.
@return <tt>true</tt> only if the edit is executed successfullly.
*/
boolean change(Prediction aPrediction, Id aPredictionListId, DateTime aToday) throws DAOException, DuplicateException {
Tx changeTx = new Change(aPrediction, aPredictionListId, aToday);
return Util.isSuccess(changeTx.executeTx());
}