BibHarvest: fix MARCXML creation in OAI updater
- Fix bug that would sometimes alternatively remove/add the OAI ID from the records to be processed upon each run of the updater.
- Clean up empty datafields from input MARCXML.
- (Re?)add support for exposing records belonging to no set (i.e. setSpec is left emtpy).
- Do not upload updated MARCXML when no record is updated.