If the backup finished in the middle of a Aria bulk load insert,
which could happen with LOAD DATA INFILE, CREATE ... SELECT etc)
there was a chance that Aria recovery would fail on the backup.

Fixed by ensuring that bulk load operations for Aria are not allowed
under BACKUP LOCK.
I also changed so that the table TRN is updated just before truncate
which ensures that old redo's for the table are ignored.
I also enabled Aria redo for DDL's to be able to repeat REPAIR commands.
Without this change recovery would not work on repaired tables.

Notes:
- We take the backup lock protection at the end of bulk insert (as we
  don't want to keep the lock over a very long running insert).
  If mariadb-backup keeps the backup lock too long,  this may fail with
  a lock timeout. In this case the batch insert will fail and the table
  will be truncated (set to it's original state).