Backport JBTM-575, javax.transaction.RollbackException root cause to EAP

In JBoss 4.2.3.GA and previous releases, when a transaction rolled back the RollbackException included the root cause of the exception. This enhancement was implemented in response to JBAS-4238 and JBTM-66.

However, in JBoss 5.1.0.GA this enhancement has been lost in some scenarios. This does not affect manual debugging (the root cause is still logged higher up in the logs), but makes it difficult for application code that relies on being able to unwrap the RollbackException to determine its root cause and therefore take appropriate action.