make RecoveryManager restartable

Stopping and restarting the transaction manager inside JBossAS causes problems, because the recovery system does not like to be restarted once it is stopped:

java.lang.IllegalThreadStateException
at java.lang.Thread.start(Thread.java:571)
at com.arjuna.ats.internal.arjuna.recovery.RecoveryManagerImple.start(RecoveryManagerImple.java:236)
at com.arjuna.ats.arjuna.recovery.RecoveryManager.startRecoveryManagerThread(RecoveryManager.java:226)
at com.arjuna.ats.jbossatx.jts.TransactionManagerService.start(TransactionManagerService.java:285)

Options would seem to be disposing the static singleton _recoveryManager in RecoveryManager and recreating it on the next start, effectively causing a new RecoveryManagerImple to be instantiated, or keep the RecoveryManagerImple instance and rework its impl so that the PeriodicRecovery _periodicRecovery is disposed and recreated on restart.

Either one has slightly odd semantics as the PeriodicRecovery is a Thread (which can't be restarted so has to be replaced) and also the object that has the module list and the server socket, so disposal and/or recreation of this state will be needed on restart. Maybe better to rename stop() to dispose() or something similarly final, to indicate the semantics are 'throw this away and start again' rather than giving the impression that stop/start == suspend/resume which is misleading.