add new utility functions to cvmfs_server
advertise repos 'in transaction' in cvmfs_server list
enable cvmfs_server rmfs for multiple repo names
enable cvmfs_server resign for multiple repo names
enable cvmfs_server transaction for multiple repo names
enable cvmfs_server abort for multiple repo names
enable cvmfs_server publish for multiple repo names
enable cvmfs_server snapshot for multiple repo names
enable cvmfs_server migrate for multiple repo names
Merge pull request #235 from reneme/multi_commands

Manipulate multiple Repositories at once with the cvmfs_server Script

This enables the following cvmfs_server commands to work on more than one repository at once:

    abort
    migrate
    publish
    resign
    rmfs
    snapshot
    transaction

One can simply list the repositories, that should be used like:
cvmfs_server rmfs -f test.local test.remote

Furthermore wildcards can be used to a certain extend like so:
cvmfs_server snapshot *.replica

For convenience the cvmfs_server list command was extended to decorate repositories currently in a transaction.