FIX: Instead of CsvBulkLoader->findExistingRecord out right failing (i.e. no duplicate found) when the duplicate check field is empty, it will now continue on to check other duplicateCheck fields.
Added extra testing data to CSVBulkLoaderTest so that it fails.
Merge pull request #1781 from jedateach/csvloader-duplicatecheck-fix

FIX: CSVBulkLoader duplicate check can now check more than one field