Improve performance

John,

This change creates two new shapefiles in spherical mercator projection. They should then render much faster since they will not longer need to be reprojected on the fly during rendering (which can be quite slow).

Also I created spatial indexes using Mapnik's `shpindex` tool. This will speed up rendering at high zoom levels by making the queries faster for the select set of points within a given tile bound.

I think this should fix the issues you've been seeing as per http://support.mapbox.com/discussions/tilemill/5301-tilemill-running-on-aws-error-message-sigkill, no need to fuss with memory settings.

Dane