Discussion with Juan on IRC ([1] through [2]) lead to this adjusted
JSON output.  Benefits over the old output include:

* deduplication (we only check the children of a given Merkle node
  once, even if multiple arguments resolve to that hash)

* alphabetized output (like POSIX's ls).  As a side-effect of this
  change, I'm also matching GNU Coreutils' ls output (maybe in POSIX?)
  by printing an alphabetized list of non-directories (one per line)
  first, with alphabetized directory lists afterwards.

[1]: https://botbot.me/freenode/ipfs/2015-06-12/?msg=41725570&page=5
[2]: https://botbot.me/freenode/ipfs/2015-06-12/?msg=41726547&page=5

License: MIT
Signed-off-by: W. Trevor King <wking@tremily.us>