the Baton generates log messages of its own, and they should get sent to the logfile, if any

When the Baton is in use and endCounter/endProcess/endProgress is called, the final state of the status line is rendered and printed as a log message. This commit provides a way for the those messages to be redirected to the log file, if there is one, without unduely coupling the Baton with the rest of reposurgeon.