RFR: Fetch PRs using the head hash

[Robin Westberg]

Hi all,

Please review this follow-up fix for faster remote repository materialization that fetches PRs by their head hash instead of a named source ref, as the ref may not be present in the remote repo.

Best regards,
Robin

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Commits:
 - 3fbb06e8: Fetch PRs using the head hash, as the source ref may not be present. Speed up move on failure.

Changes: https://git.openjdk.java.net/skara/pull/417/files
 Webrev: https://webrevs.openjdk.java.net/skara/417/webrev.00
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/skara/pull/417.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/417/head:pull/417

PR: https://git.openjdk.java.net/skara/pull/417