RFR: 1350: Altfixversions isn't checking Backport resolution

[Erik Joelsson]

This patch fixes a flaw in the altfixversion feature. Currently a backport with an altfixversion is considered valid if the state is "resolved". There are two problems with this. It misses backports that are in state closed. It could also cause false positives by accepting backports that aren't set to resolution "Fixed".

To fix this, I've introduced a new method on the Issue interface "isFixed()". The default implementation (which will get used in testing) just delegates to isResolved(). For JiraIssue, it checks both the state and the resolution.

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Commit messages:
 - SKARA-1350

Changes: https://git.openjdk.java.net/skara/pull/1286/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1286&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-1350
  Stats: 28 lines in 3 files changed: 24 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/skara/pull/1286.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1286/head:pull/1286

PR: https://git.openjdk.java.net/skara/pull/1286