RFR: 568: RFR mails from the list are not copied to github

[Robin Westberg]

The mbox parser could fail to pick up replies that were out of order, as well as replies with additional text in the In-Reply-To header.

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Commit messages:
 - Improve mbox parsing

Changes: https://git.openjdk.java.net/skara/pull/1095/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1095&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-568
  Stats: 120 lines in 2 files changed: 95 ins; 2 del; 23 mod
  Patch: https://git.openjdk.java.net/skara/pull/1095.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1095/head:pull/1095

PR: https://git.openjdk.java.net/skara/pull/1095