Patch to spark-jobserver to clean up GC

gistfile1.scala

    case StopContext(name) =>
      if (contexts contains name) {
        logger.info("Shutting down context {}", name)
        context.watch(contexts(name))   // watch for termination event
        contexts(name) ! PoisonPill
        contexts.remove(name)
        resultActors.remove(name)
        sender ! ContextStopped
      } else {
        sender ! NoSuchContext
      }

    case Terminated(name) =>
      // Child JobManagerActor actually cleaned up
      logger.info("context {} cleaned up, invoking GC to free permgen/classes...", name)
      // For details see https://github.com/sbt/sbt/issues/1223
      System.gc(); java.lang.System.runFinalization(); System.gc()

For LocalContextSupervisorActor