This patch allows the user to override the current git repository's origin URL by setting --repository_url.

We use this where I work with a custom ReviewBoard/Github:FI integration. We have canonical repos in Github that contributors fork. Contributors work in their fork while a script on the ReviewBoard server clones the canonical repo and adds a remote/fetches commits for every fork so that ReviewBoard has access to all commits.

The repository URL that our integration needs in order to use post-review is the canonical repo, and not the fork. --repository-url seems like a reasonable entry point to add this functionality.

In use in our organization by our engineering group.