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.

*** 1338,1347 ****
--- 1338,1353 ----
          dmu_send.o              \
          dmu_object.o            \
          dmu_objset.o            \
          dmu_traverse.o          \
          dmu_tx.o                \
+         fits.o                  \
+         fits_pass1.o            \
+         fits_pass2.o            \
+         fits_send.o             \
+         fits_crc32c.o           \
+         fits_count.o            \
          dnode.o                 \
          dnode_sync.o            \
          dsl_dir.o               \
          dsl_dataset.o           \
          dsl_deadlist.o          \