Implement
* pruning on source side
* local job
* test subcommand for doing a dry-run of a prune policy
* use a non-blocking callback from autosnap to trigger the depending
jobs -> avoids races, looks saner in the debug log
Don't use jobrun for daemon, just call JobDo() once, the job must
organize stuff itself.
Sacrifice all the oneshot commands, they will be reintroduced as
client-calls to the daemon.
