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.

*** 200,209 ****
--- 200,210 ----
  int dsl_dataset_own(const char *name, boolean_t inconsistentok,
      void *tag, dsl_dataset_t **dsp);
  int dsl_dataset_own_obj(struct dsl_pool *dp, uint64_t dsobj,
      boolean_t inconsistentok, void *tag, dsl_dataset_t **dsp);
  void dsl_dataset_name(dsl_dataset_t *ds, char *name);
+ int dsl_dataset_namelen(dsl_dataset_t *ds);
  void dsl_dataset_rele(dsl_dataset_t *ds, void *tag);
  void dsl_dataset_disown(dsl_dataset_t *ds, void *tag);
  void dsl_dataset_drop_ref(dsl_dataset_t *ds, void *tag);
  boolean_t dsl_dataset_tryown(dsl_dataset_t *ds, boolean_t inconsistentok,
      void *tag);