BITMAG-1042: Added the checksum states PREVIOUSLY_SEEN and MISSING, and methods for using them.
Setting new files to missing checksum, etc.
Added 'Missing' checksum to some checks.
Added test and made smaller fix.
BITMAG-1042: Added the file with tests for the new states.
BITMAG-1042: Followup on CR-BITMAG-314
Merge branch 'master' into BITMAG-1042
Merge branch 'master' into BITMAG-1063
Fixed merge issue.