fixes #3407, prevent NPE
Merge branch 'master' of https://github.com/hazelcast/hazelcast
Merge branch 'master' of https://github.com/hazelcast/hazelcast
also take backups of tx reservations
removed prevent NPE fix
small cleanup
Merge pull request #3436 from ahmetmircik/fix/3.3/txReservationBackups

Also take backups of reservations before prepare phase in transactional queue implementation