RFR: vcs: don't append newlines to tag messages

[Erik Helin]

Hi all,

please review this small patch that ensures that neither git nor hg append any newlines to message used when creating
annotated tag objects.

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

Thanks,
Erik

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Commit messages:
 - vcs: don't append newlines to tag messages

Changes: https://git.openjdk.java.net/skara/pull/734/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=734&range=00
  Stats: 4 lines in 3 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/skara/pull/734.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/734/head:pull/734

PR: https://git.openjdk.java.net/skara/pull/734