JCA recovery race condition

Evidenced in SimpleIsolatedServers::testSimultaneousRecovery

Basically XATerminatorImple -> SAA::activate() -> XAResourceRecord::restore_state() -> getNewXAResource() -> XARecoveryModule::getNewXAResource()

At this point _xidScans may be none-null but still only partial from the first scan: periodicWorkSecondPass -> bottomUpRecovery -> resourceInitiatedRecoveryForRecoveryHelpers -> xaRecovery

if (_xidScans == null)
_xidScans = new Hashtable<XAResource,RecoveryXids>();

What I am not sure of is whether we should synchronize bottomUpRecovery and getNewXAResource as that would stop this race condition. Gonna give that a whirl.