make box2d<T> adapters more generic.
make box2d<T> adapters more generic.

tomhughes/mapnik,naturalatlas/mapnik,tomhughes/mapnik,mapnik/mapnik,tomhughes/mapnik,lightmare/mapnik,lightmare/mapnik,mapnik/mapnik,naturalatlas/mapnik,lightmare/mapnik,tomhughes/mapnik,mapnik/mapnik,mapnik/mapnik,naturalatlas/mapnik,naturalatlas/mapnik,lightmare/mapnik