FIX: unnecessary grep in check_tag_existence()
FIX: unnecessary grep in check_tag_existence()

Moliholy/cvmfs,cvmfs/cvmfs,trshaffer/cvmfs,alhowaidi/cvmfsNDN,reneme/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,trshaffer/cvmfs,djw8605/cvmfs,trshaffer/cvmfs,Moliholy/cvmfs,alhowaidi/cvmfsNDN,Gangbiao/cvmfs,Gangbiao/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,reneme/cvmfs,alhowaidi/cvmfsNDN,djw8605/cvmfs,djw8605/cvmfs,alhowaidi/cvmfsNDN,DrDaveD/cvmfs,DrDaveD/cvmfs,Gangbiao/cvmfs,djw8605/cvmfs,trshaffer/cvmfs,Gangbiao/cvmfs,reneme/cvmfs,cvmfs/cvmfs,djw8605/cvmfs,cvmfs/cvmfs,reneme/cvmfs,alhowaidi/cvmfsNDN,Gangbiao/cvmfs,reneme/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,Moliholy/cvmfs,trshaffer/cvmfs,Moliholy/cvmfs,Moliholy/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs