Create --after and/or --range options for zfs-delete-snapshots

[joelweinberger]

Currently, we have options for deleting all snapshots up to a given snapshot and for deleting all snapshots across datasets matching a specified snapshot. Another set of useful options might be ones that specify the deletion of all snapshots after a given snapshot or all snapshots between two given snapshots. These would be mutually exclusive with --upto.

[joelweinberger]

Thinking about this further, really it only makes sense to have a --range option. I think that --after would probably just be equivalent to a rollback...

[joelweinberger]

Further suggestion: make the second argument to the incremental flag optional. If not specified, deletes all snapshots from the specified snapshot to the current snapshot (exclusive of current).

[joelweinberger]

This is added in f80e09e. I did not make the argument to the --range flag optional, however. Frankly, I couldn't figure out how to reasonably implement that. Perhaps for another day, but I also don't think it matters all that much.