Update error handling of mongo insert duplicates -- this is caused by the way the batching system works. If a worker sees an entry more than once in the same bulk 'batch' it won't know that the entry has already been processed. Also, added some related code to process_entry to check the current entry version number -- if it matches the passed in identifier, it doesn't bother processing the entry. This condition would be met if there are two entries in the csvs that fall into different bulk sets