dinghy: "chown: operation not permitted" error mounting host volume for Postgres.

We have a Docker project that uses a Postgres container (postgres:9.3 image) with /var/lib/postgresql/data mounted to the local filesystem, and it works fine on Linux, but errors out on Mac with “chown: operation not permitted”. boot2docker was running into permissions issues there as well, which is why we first tried dinghy, though boot2docker’s errors were more confusing.