code: func NewImageWriter(am schema.ImageManifest, w *tar.Writer) aci.ArchiveWriter {
  	aw := &imageArchiveWriter{
  		w,
  		&am,
  	}
  	return aw
  }
docs: // NewImageWriter creates a new ArchiveWriter which will generate an App
  // Container Image based on the given manifest and write it to the given
  // tar.Writer
  // TODO(sgotti) this is a copy of appc/spec/aci.imageArchiveWriter with
  // addFileNow changed to create the file with the current user. needed for
  // testing as non root user.