anchor.diff:     * Checks out the reference [ref] in [repoPath].
      */
     Future _checkOut(String repoPath, String ref) {
  -    return runProcess("git", ["checkout", ref], pipeStdout: true,
  -        pipeStderr: true, workingDir: repoPath).transform((result) {
  +    return runProcess("git", ["checkout", ref], workingDir: repoPath)
  +        .transform((result) {
         if (!result.success) throw 'Git failed.';
         return null;
       });
  
positive.code:    * Clones the repo at the URI [from] to the path [to] on the local filesystem.
     */
    Future _clone(String from, String to) {
      return runProcess("git", ["clone", from, to], pipeStdout: true,
          pipeStderr: true).transform((result) {
        if (!result.success) throw 'Git failed.';
        return null;
      });
  
negative.code:     return exists(path).chain((exists) {
        if (!exists) return _clone(_getUrl(id), path);
  
        return runProcess("git", ["pull", "--force"], workingDir: path)
            .transform((result) {
          if (!result.success) throw 'Git failed.';
          return null;
        });
  