Made import failures slightly more comprehensible
Made import failures slightly more comprehensible

MetGIS/TileStache,MetGIS/TileStache,Kosta-Github/TileStache,SEL-Columbia/TileStache,Billups/TileStache,moskvax/TileStache,mapzen/TileStache,robpvn/Vector-Tile-Research,mojodna/TileStache,SEL-Columbia/TileStache,Billups/TileStache,MetGIS/TileStache,TileStache/TileStache,TileStache/TileStache,jbants/TileStache,mapzen/TileStache,SEL-Columbia/TileStache,Kosta-Github/TileStache,robpvn/Vector-Tile-Research,Billups/TileStache,jbants/TileStache,Blechhirn/TileStache,mpuig/TileStache,Blechhirn/TileStache,Kosta-Github/TileStache,moskvax/TileStache,Blechhirn/TileStache,mapzen/TileStache,mojodna/TileStache,robpvn/Vector-Tile-Research,TileStache/TileStache,moskvax/TileStache,mpuig/TileStache,jbants/TileStache