RFR: Make it possible to only allow PRs against a select set of target branches

[Robin Westberg]

Hi all,

Please review this change that makes it possible to only allow PRs to target a select set of branches.

Best regards,
Robin

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Commits:
 - 7c3c3098: Make it possible to only allow PRs against a select set of target branches

Changes: https://git.openjdk.java.net/skara/pull/377/files
 Webrev: https://webrevs.openjdk.java.net/skara/377/webrev.00
  Stats: 130 lines in 6 files changed: 99 ins; 18 del; 13 mod
  Patch: https://git.openjdk.java.net/skara/pull/377.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/377/head:pull/377

PR: https://git.openjdk.java.net/skara/pull/377