Catch and report duplicate column names in header line (add CsvReadFeature.FAIL_ON_DUPLICATE_HEADER_COLUMNS) (original) (raw)

(note: offshoot of a comment in #285)

It looks like code does not currently check that the column names included in the header line are unique; meaning that one name may be occur more than once, and in that case the last one is used.
This should not be allowed: column names in header line should not have duplicates.