RFR: 365: Allows "merge style" PRs to have title of "Merge repo:tag"

[Robin Westberg]

Hi all,

Please review this change that improves the merge sourcing for merge PRs and allows tags to be used as a source.

Best regards,
Robin

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

Commit messages:
 - Improve merge source parsing, add tag support

Changes: https://git.openjdk.java.net/skara/pull/610/files
 Webrev: https://webrevs.openjdk.java.net/skara/610/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-365
  Stats: 176 lines in 3 files changed: 119 ins; 30 del; 27 mod
  Patch: https://git.openjdk.java.net/skara/pull/610.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/610/head:pull/610

PR: https://git.openjdk.java.net/skara/pull/610