Shivaram, it seems a little scary to modify `compute-classpath` to always include binary class files if they are present.

What if a user has both (a) compiled classes of spark and (b) the normal compiled assembly that includes spark? Like say someone has downloaded a pre-built version of Spark, then they do some modifications and `compile`. Which will take precedence? Maybe I'm misunderstanding but it seems like this would result in somewhat confusing behavior.

It might be safer to have a flag or environment variable that a developer explicitly has to set which will cause dependencies to be included in this way.