hey @sryza - would this still be necessary if we merged the patch that makes `addJar` load the jar at the driver in addition to the executors? I'm a little bit wary of having yet another way to add runtime dependencies. It seems as we simplify this we're moving towards (a) you use addJar when launching in a client mode and (b) you use the launch scripts ala the YARN launcher when running in a cluster mode. Is that not sufficient in some case?