RFR: git-sync: use ref names instead of hashes

[Erik Helin]

Hi all,

please review this small patch that makes `git sync` avoid using SHA-1 hashes
when executing `git fetch`. There was nothing wrong with this approach, but
older `git` clients have problems when the ref to fetch is a SHA-1 hash. There
is no drawback in using the ref name instead, it only increases compatibility
with older `git` clients.

Thanks,
Erik

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Commits:
 - ad941e54: git-sync: use ref names instead of hashes

Changes: https://git.openjdk.java.net/skara/pull/408/files
 Webrev: https://webrevs.openjdk.java.net/skara/408/webrev.00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/408.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/408/head:pull/408

PR: https://git.openjdk.java.net/skara/pull/408