RFR: git: commitMetadata should return commits in topo order

[Erik Helin]

Hi all,

please review this small patch that makes `GitRepository.commitMetadata` return commits topological order (i.e. all
parents first, then the parent). This is already done by `GitRepository.commits`.

Testing:
- [x] `make test` passes on Linux x64
- [ ] Did not add a new unit test since it is hard to force commits to be returned in non-topological order

Thanks,
Erik

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Commit messages:
 - git: commitMetadata should return commits in topo order

Changes: https://git.openjdk.java.net/skara/pull/727/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=727&range=00
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/skara/pull/727.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/727/head:pull/727

PR: https://git.openjdk.java.net/skara/pull/727