Early abort, failing to allocate buffers, would go down the abort track and
 end up trying to sendDropTriggers (as the standard stop backup does). 
However, it is possible to not have any tables yet defined in the backup 
(due to allocating buffers is before this). Simple check in sendDropTrig 
(and continue to next step). Files may be open, so we continue to close them.

Also updated ERROR_Codes (and added one to test this bug).


storage/ndb/src/kernel/blocks/ERROR_codes.txt:
  update BACKUP error insert codes to reflect current reality.
storage/ndb/src/kernel/blocks/backup/Backup.cpp:
  Allow for early abort when no tables have been included in backup.
  
  Allow for abort when file records have been seized but not yet allocated
  to specific uses (is the case when buffer allocation fails)
storage/ndb/src/kernel/blocks/backup/Backup.hpp:
  initialize BackupRecord file Ptrs
storage/ndb/test/src/NdbBackup.cpp:
  Add extra failure codes for buffer allocation failure in backup