search for: zfs_ioc_fits_send

We have finished a beta version of the feature. A webrev for it can be found here: http://cr.illumos.org/~webrev/sensille/fits-send/ It adds a command ''zfs fits-send''. The resulting streams can currently only be received on btrfs, but more receivers will follow. It would be great if anyone interested could give it some testing and/or review. If there are no objections,