offline mode, and then test to see if the file-based basedir for an artifact
  repository works...if it doesn't work, we can mark that repository offline...

  OTOH, all offline-mode checks can probably be run from Wagon-based APIs.

** Maven-SCM

  In all but trivial examples, SCM operations cannot complete without
  having access to the versioning server. Therefore, it is assumed that

        try {
            return repo.getLayout().getId();
        } catch (LinkageError e) {
            /*
             * NOTE: getId() was added in 3.x and is as such not implemented by plugins compiled against 2.x APIs.
             */
            String className = repo.getLayout().getClass().getSimpleName();
            if (className.endsWith("RepositoryLayout")) {