Somewhere between Bruce's and Steve's information lies this: Herbert Hughes' version was published early in 20th century, titled "The Next Market Day" and qualified thus - ‘Fragment of Tyrone Ballad, adapted’. Patently Hughes fiddled, Bruce thought Bowdlerised but we'll pass that over. However, while Comber is a toponym in Ireland, there can be no possible reasons for locating the song there but that Comber was the centre of a flax growing area and that the comber of the Comber's/Carman's whistle is homophonic with Comber. Hence, I'd stick at least partly with what he (Bruce) said - which is always a good idea!