RFR: vcs: only convert tags that are part of branch

[Erik Helin]

Hi all,

please review this patch that ensures that the `GitToHgConverter` only converts tags that are pointing to commits on the branch the converter is converting.

Thanks,
Erik

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Commit messages:
 - checkout: only convert tags that are part of branch

Changes: https://git.openjdk.java.net/skara/pull/988/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=988&range=00
  Stats: 7 lines in 1 file changed: 7 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/skara/pull/988.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/988/head:pull/988

PR: https://git.openjdk.java.net/skara/pull/988