FIX: race - trap register and sentinel creation
FIX: race - trap register and sentinel creation

trshaffer/cvmfs,reneme/cvmfs,Moliholy/cvmfs,trshaffer/cvmfs,Moliholy/cvmfs,alhowaidi/cvmfsNDN,DrDaveD/cvmfs,trshaffer/cvmfs,cvmfs/cvmfs,Gangbiao/cvmfs,alhowaidi/cvmfsNDN,djw8605/cvmfs,reneme/cvmfs,Moliholy/cvmfs,djw8605/cvmfs,MicBrain/cvmfs,cvmfs/cvmfs,Gangbiao/cvmfs,cvmfs-testing/cvmfs,MicBrain/cvmfs,djw8605/cvmfs,cvmfs/cvmfs,alhowaidi/cvmfsNDN,DrDaveD/cvmfs,alhowaidi/cvmfsNDN,cvmfs-testing/cvmfs,Gangbiao/cvmfs,alhowaidi/cvmfsNDN,Moliholy/cvmfs,trshaffer/cvmfs,cvmfs/cvmfs,cvmfs-testing/cvmfs,trshaffer/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,reneme/cvmfs,MicBrain/cvmfs,cvmfs/cvmfs,cvmfs-testing/cvmfs,cvmfs/cvmfs,reneme/cvmfs,Gangbiao/cvmfs,Gangbiao/cvmfs,djw8605/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,MicBrain/cvmfs,MicBrain/cvmfs,DrDaveD/cvmfs,reneme/cvmfs,Moliholy/cvmfs,djw8605/cvmfs,cvmfs-testing/cvmfs