add SQL for filtering original files by repository
add repository DAO method for filtering files by repository
add API method for setting files' checksum
genericize Executor.Work

would be nice to do in general with Executor but that's a larger job
implement new repository method
test new repository method
add API documentation note about checking existing hashes
remove executor from managed repository
move worker creators into repository DAO methods
Merge remote-tracking branch 'remotes/origin/develop' into trac-10766-change-hasher
make code slightly clearer
remove accidental imports
add repository method for verifying file checksums
add warning to docs about setting files' checksum algorithm
make checksum verification case-insensitive

If implementation of checksum algorithm changes to record
hexadecimal differently, would be most tiresome to have to
accompany with upgrade script for a simple case chage.
add integration test for ManagedRepository.verifyChecksums
Merge pull request #2884 from mtbc/trac-10766-change-hasher

fix #10766: add API method for changing original files' hasher