Improve update SQL for IntegrityService database

Several places in the IntegrityDAO the following kind of updates are used:
UPDATE ...
WHERE file_key IN (SELECT ... FROM files WHERE ...)

It can be a very heavy operation, since it potentially may need to have an enti
This can be improved by using a JOIN instead. Probably a INNER JOIN.
But that kind of UPDATE-JOIN seems to work differently on different databases, so it probably needs database-specific implementations.

(Found in review CR-BITMAG-314).