RFR: Upgrade the notifier database lazily

[Robin Westberg]

Hi all,

Please review this change that updates the notifier database for pull requests only for active PRs.

Best regards,
Robin

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Commit messages:
 - Upgrade the notifier database lazily

Changes: https://git.openjdk.java.net/skara/pull/657/files
 Webrev: https://webrevs.openjdk.java.net/skara/657/webrev.00
  Stats: 24 lines in 1 file changed: 11 ins; 7 del; 6 mod
  Patch: https://git.openjdk.java.net/skara/pull/657.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/657/head:pull/657

PR: https://git.openjdk.java.net/skara/pull/657