Branch Compare: the target branch's repository is ignored

If the target branch's repository is a different repository from the source, the repository is ignored. More precisely, the branch is resolved as it was a ref on the source repository.

By definition, synchronized repositories are usually unaffected except if the branch diverged between the source and target repositories.

The cause is that the end point for the commit list (used by the repository commit list and reused by the Branch Compare UI) only deferences ref names according to the primary repository, even if the information about a secondary repository is sent.