in src/main/scala/com/twitter/stitch/Stitch.scala [1793:1798]
private[stitch] def app[T, U](f: T => Stitch[U], t: T): Stitch[U] =
try f(t)
catch {
case e: NonLocalReturnControl[_] => exception(new StitchNonLocalReturnControl(e))
case NonFatal(e) => exception(e)
}