No need to specify the repository name in `cvmfs_server add-replica`

Until now, one needed to specify the repository name when calling `cvmfs_server add-replica` even though it was requested to be equal to the repository name in Stratum 0. This patch allows the script to figure out the repository name from the .cvmfspublished file downloaded from Stratum 0.

Note: This Pull Request also includes [this one](https://github.com/cvmfs/cvmfs/pull/68).