review row counting in CSVKitWriter

Created by: JoeGermuska

FWIW, in implementing the DictReader/DictWriter I exposed the line numbering that is inherent in csv.reader https://github.com/JoeGermuska/csvkit/commit/ce107151c020b5bf822ba50004a285bd976ea447#L0R52 (I hadn't known it was in there)

This seems to make some of this https://github.com/onyxfish/csvkit/blob/master/csvkit/__init__.py#L20 obsolete.

I figured I'd just note it now. It's a small deal, but it would be best if all the code were aware of the other bits of the code!