yeah I think I like Pierre's suggestion.   I think in the beginning I threw the exception b/c there was no `ArgMain`, and other than throwing an exception, there isn't much you can do.  I don't like `System.exit` for the reasons Pierre suggests.  But now that `ArgMain` can handle it, that seems like a better solution.

I wonder -- should we throw an exception without a stack trace?  http://www.scala-lang.org/files/archive/nightly/docs/library/index.html#scala.util.control.NoStackTrace

maybe that stack trace is still useful when its not getting caught in `ArgMain`.