RFR: hg: implement hashes for blobs for ls-tree

[Erik Helin]

Hi all,

please review this patch that properly implements `ls-tree` for Mercurial.

Testing:
- [x] `make test` passes on Linux x64
- [x] Updated unit test

Thanks,
Erik

-------------

Commit messages:
 - hg: implement hashes for blobs for ls-tree

Changes: https://git.openjdk.java.net/skara/pull/725/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=725&range=00
  Stats: 12 lines in 2 files changed: 10 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/725.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/725/head:pull/725

PR: https://git.openjdk.java.net/skara/pull/725