Link `cvmfs_receiver` with RT_LIBRARY to fix Travis-CI on Ubuntu 12.04
Link `cvmfs_receiver` with RT_LIBRARY to fix Travis-CI on Ubuntu 12.04

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