Initial work for adding a whenCompleted method to Status. It works in the
two stateful statuses.
Renamed StatusSpec to StatefulStatusSpec
Implemented whenCompleted in SucceededStatus and FailedStatus, and changed the
spec to not execute the functions in order of registration.
Added two tests that already passed ensuring that multiple registered
callbacks are executed by the stateful statuses.
Added some more tests that already passed that ensure that multiple
functions registered with whenCompleted on SucceededStatus and
FailedStatus run.
Implemented whenCompleted in CompositeStatus.
Merge branch 'master' of https://github.com/scalatest/scalatest