expose a magic file while stratum1 snapshotting is running
set locale in cvmfs_server (calls to 'date')
remove the magic file even when a SIGNAL appears
Merge pull request #307 from reneme/snapshotting_magic_file

Expose a Magic File While Stratum1 Snapshotting is Running

This exposes a magic file called .cvmfs_is_snapshotting in the repository root while the snapshot procedure is running. Monitoring tools can use that to show nice spinner-animations while replication is in progress. Initially I put this status information in the mini-REST-API but it would be nice to have this information, even if the stratum 1 administrator decides to not expose the REST-API at all.