Code review comment for lp:~cjwatson/launchpad/git-defaults

I'm not sure about the target.getDefaultGitRepository/setDefaultGitRepository design. They're yet more domain-specific methods on already huge Registry classes, which just isn't maintainable long-term.

During Disclosure we experimented with SharingService to stop the bloat, which ended up hideous more because of the different artifact types than because of a fundamental issue with the service concept.