changelogging: exclude new modified_date field from log record trigger comparison

when we construct triggers for changelogging, we compare the OLD/NEW record data to see if a change actually occurred, and only trigger a log record if so.

with the addition of the modified_date field in 4.3, we should exclude that from the comparison. simply editing/saving a record currently results in a changelog record because of the different modified date, but should not be considered a substantive change worth logging.