Mapnik Update

Artem Pavlenko's Mapnik continues to advance, and I'm still trying to keep an eye on this as a another potential rendering engine for PCL and PrimaGIS. Agg, Boost, thread-safety ... I welcome this, but since he's starting mostly from scratch, there is a bit of catching up yet to do. While simple, Artem's Hello World demonstrates again how good Agg can be for producing clean looking maps. Would be great to see some other layers, and examples of the feature-level transparency that MapServer lacks.