FAR: generating send-streams in portable format
This commit adds a switch '-F' to  zfs send. This set, zfs send generates
a stream in FAR-format instead of the traditional zfs stream format. The
generated send stream is compatible with the stream generated from 'btrfs send'
and can in principle easily be received to any filesystem.

*** 583,592 ****
--- 583,595 ----
          /* parsable verbose output (ie. -P) */
          boolean_t parsable;
  
          /* show progress (ie. -v) */
          boolean_t progress;
+ 
+         /* send output as FAR-stream */
+         boolean_t far;
  } sendflags_t;
  
  typedef boolean_t (snapfilter_cb_t)(zfs_handle_t *, void *);
  
  extern int zfs_send(zfs_handle_t *, const char *, const char *,