If a developer intends to do a backport and references the original bug/issue, Skara will complain: "Issue is not open". This is technically correct, since the original issue is closed, but it is not very helpful.

The developer is supposed to instead open a "backport-style" PR, meaning the PR title should be "Backport <hash>" with the hash of the git commit that solved the original bug. In most cases, this is the right thing to do, even if the backport does not apply cleanly, and it is regardless of if the PR was created using the Skara PR/commit command `/backport`.

Instead, we should output something along these lines:

JDK-nnnnnnn is already resolved. Please consider using a Backport-style pull request, i.e. set the PR title to `Backport <hash>` with the hash of the original fix.

... and possibly link to documentation on how to do backports (Skara or the Developers Guide?)