Page no 46 of "ejb-3_0-fr-spec-persistence.pdf" Entity Operaions
* Indicate to the EntityManager that a JTA transaction is
* active. This method should be called on a JTA application
* managed EntityManager that was created outside the scope
* of the active transaction to associate it with the current
* JTA transaction.
* @throws TransactionRequiredException if there is
* no transaction.
public void joinTransaction();