Skara Backports handling needs to handle non backport type as backport

Sometimes people make mistakes and connect bugs with backport links in JBS where both sides are of types other than Backport. This shouldn't be encouraged behavior, but when it happens, Skara currently fails to handle it. Since this is a valid (though undesirable) state in JBS, Skara needs to be able to handle it.

Specifically, when querying for all backports for an issue, Skara should stop filtering out issues with a different type and just honor the "backported by" link.