fix auto tag cleanup for very long tag lists (ported from 2.3)
fix auto tag cleanup for very long tag lists (ported from 2.3)

cvmfs/cvmfs,DrDaveD/cvmfs,djw8605/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,djw8605/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,Gangbiao/cvmfs,DrDaveD/cvmfs,djw8605/cvmfs,Gangbiao/cvmfs,DrDaveD/cvmfs,Gangbiao/cvmfs,djw8605/cvmfs,Gangbiao/cvmfs,DrDaveD/cvmfs,Gangbiao/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,djw8605/cvmfs