So this is the only nit pick I have in the whole patch.  Now Local is parameterized by a Hadoop object, Configuration.  Feels like the right thing to do here would be to parameterize it with whatever Cascading local mode uses, which I think is Map[String, String] (but may be Properties).

However, I think this only matters if scalding ever gets carved into scalding-core, scalding-hadoop, and scalding-local, which doesn't seem to be eminent or necessary.  We can refactor later if we care to.