FITS: generating send-streams in portable format
This commit adds the command 'zfs fits-send', analogous to zfs send. The
generated send stream is compatible with the stream generated with that
from 'btrfs send' and can in principle easily be received to any filesystem.

*** 1191,1200 ****
--- 1191,1202 ----
                  "zfs_cmd_t" },
          { (uint_t)ZFS_IOC_RECV,                 "ZFS_IOC_RECV",
                  "zfs_cmd_t" },
          { (uint_t)ZFS_IOC_SEND,                 "ZFS_IOC_SEND",
                  "zfs_cmd_t" },
+         { (uint_t)ZFS_IOC_FITS_SEND,            "ZFS_IOC_FITS_SEND",
+                 "zfs_cmd_t" },
          { (uint_t)ZFS_IOC_INJECT_FAULT,         "ZFS_IOC_INJECT_FAULT",
                  "zfs_cmd_t" },
          { (uint_t)ZFS_IOC_CLEAR_FAULT,          "ZFS_IOC_CLEAR_FAULT",
                  "zfs_cmd_t" },
          { (uint_t)ZFS_IOC_INJECT_LIST_NEXT,     "ZFS_IOC_INJECT_LIST_NEXT",