Exclude restored dataset from further backup if restored to an alternate name

[esproul]

Unless we are restoring a backup to the same host and name from which it originated, we should probably default to excluding the restored backup to avoid backing it up again under the new name.

I'm not sure whether this is really what we want, but in my experience, if I'm restoring under an alternate name, it's so that I can reference something from the backup, and I don't actually want the alternate copy backed up again. I think the fact that the hostname and/or dataset name differ from the original should be a reasonable indicator. In that case, the restore should set the exclude property on the restored dataset as a final step before completion.