PT should warn if fill/fetch overwrites existing attribute text

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Just had an instance where I had forgotten to disable fetching of a child class for which I was intending to provide static values (msn:product_type_name, to be exact). Only noticed that PT was fetching (and thus overwriting) my static value when the product was being loaded as it's ancestor by my processor.

This is a case where human error very easily can creep in, and we should at least provide debug log records when this occurs. Yes, this should have been (and eventually was) caught in QA, but PDS4 labels are verbose beasts and PT should do everything possible to highlight potential mistakes like this.