anchor.diff:     * 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) {
  +    return runProcess("git", ["clone", from, to]).transform((result) {
         if (!result.success) throw 'Git failed.';
         return null;
       });
  
positive.code:     return exists(path).chain((exists) {
        if (!exists) return _clone(_getUrl(id), path);
  
        return runProcess("git", ["pull", "--force"], workingDir: path,
            pipeStdout: true, pipeStderr: true).transform((result) {
          if (!result.success) throw 'Git failed.';
          return null;
        });
  
negative.code:    */
    Future<String> _revisionAt(PackageId id) {
      return runProcess("git", ["rev-parse", _getEffectiveRef(id)],
          workingDir: _repoCachePath(id)).transform((result) {
        if (!result.success) throw 'Git failed.';
        return result.stdout[0];
      });
  