small optimisation: don't pass back the stdout text unless it will be printed (which is only if in debug mode)
cleaner implementation of cucumber resetting to run new features
refactor workers to reduce duplication
standardise debug logging of master <-> runner <-> worker activity a bit more - log from the master rather than making an extra network trip to send the log.  rename "next" command to the master to "next_file" as it can now be a straight passthrough from the worker.