RFR: Add support for adding extra headers to mails sent to mailing lists

[Robin Westberg]

Hi all,

Please review this change that allows adding extra headers to mails that are sent to mailing lists. This can be used to add authentication headers.

Best regards,
Robin

----------------

Commits:
 - 7fcd00bc: Add support for adding extra headers to mails sent to mailing lists

Changes: https://git.openjdk.java.net/skara/pull/158/files
 Webrev: https://webrevs.openjdk.java.net/skara/158/webrev.00
  Stats: 32 lines in 5 files changed: 16 ins; 0 del; 16 mod
  Patch: https://git.openjdk.java.net/skara/pull/158.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/158/head:pull/158

PR: https://git.openjdk.java.net/skara/pull/158