Provide a management interface to see a list of Xids that are being being considered for recovery by the recovery manager

Although it is possible to see the list of current transactions in the CLI, for those branches that are available for recovery it can be useful to see the list that the recovery manager is considering. I have often looked in the debugger at this state:
https://github.com/jbosstm/narayana/blob/master/ArjunaJTA/jta/classes/com/arjuna/ats/internal/jta/recovery/arjunacore/XARecoveryModule.java#L1017 so it might be useful to others.