don't use ST_Centroid
don't use ST_Centroid

Using pgfourine, I found that ST_Centroid is really slow, it is much better
to pass the full polygon to mapnik.

Even though I've declared the layers to geometry point, it still seems to work
fine for queries that retrieve both points and polygons.

andrewharvey/osm-hybrid-carto,andrewharvey/osm-hybrid-carto,andrewharvey/osm-hybrid-carto