title: Exit code for sbt project
body: <p>I have a project, build with sbt and using akka actors. I run it with "sbt 'run $args'" command and I want this program to return different exit codes depending on some condition. I use System.exit(code) from my main actor for this purposes. <br>
  Problem, I can`t solve is that sbt exit code depends on program arguments: sometimes it exits with error</p>
  
  <pre><code>java.lang.RuntimeException: Nonzero exit code returned from runner: 3        at scala.sys.package$.error(package.scala:27)
  [trace] Stack trace suppressed: run last compile:runMain for the full output.
  [error] (compile:runMain) Nonzero exit code returned from runner: 3
  [error] Total time: 5 s, completed Dec 4, 2014 6:50:50 PM
  </code></pre>
  
  <p>that is not beauty, but that's ok.<br> 
  But in some conditions I run System.exit(3), but sbt exits with 0 exit code and [success] message.<br>
  It there a way to force sbt to exit with the same code as my program?<br>
  P.S. I`m not sure, but looks like main difference between arguments is that in first case program is executed in one thread and in the second case it executed in more then 1 thread</p>