ImageTypeConversion needs to call set_host_dirty()
ImageTypeConversion needs to call set_host_dirty()

Also, most the set_host_dirty() call for load_png into the host load() call, so all load implementations benefit from it.

kgnk/Halide,psuriana/Halide,kgnk/Halide,kgnk/Halide,kgnk/Halide,kgnk/Halide,kgnk/Halide,kgnk/Halide,psuriana/Halide,psuriana/Halide,psuriana/Halide,psuriana/Halide,psuriana/Halide,psuriana/Halide,kgnk/Halide