Use new CVMFS_MAGIC_XATTRS_VISIBILITY option for publisher client
Use new CVMFS_MAGIC_XATTRS_VISIBILITY option for publisher client

This is just for future-proofing. There is no need to migrate existing
repostories because the old CVMFS_HIDE_MAGIC_XATTRS still works as
before.

DrDaveD/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs