print a simple version number with cvmfs_swissknife --version OR cvmfs_swissknife version
add checking of repository compatibility across versions
added a migration mechanism to update repositories to 2.1.7
cosmetics
Merge pull request #85 from reneme/auto_update

Migrating old Repositories to current version

    - This checks if a repository is compatible to the currently installed CernVM-FS version and warns the user in case of incompatibility.
    - Furthermore it allow to update the repository by calling cvmfs_server migrate
    - From now on server.conf contains CVMFS_CREATOR_VERSION to make the migration process easier in the future
    - cvmfs_server list shows the version of the creator when it differs from the current version
    - migration should be flexible enough to work transitively: 2.1.6 -> 2.1.7 -> 2.1.8 in one run

Known issue: It can only handle 2.1.x repositories. Migration from 2.0.x is not supported atm.