Fixes T4041. We currently detect when "origin" is incorrect, but can do better:

• When "origin" is missing, we can add it. This happens for Git 1.7.1 -- see T4041.
• When "origin" is wrong, we can fix it automatically if we control the repository.

We only need to fail when origin exists, is wrong, and we aren't in charge of the repository.

Ran bin/repository discover X on a repository with a good origin, no origin, a bad-but-under-control origin, and a bad-out-of-control origin. Got the right behavior in all cases.