def add_file(file)
      @tarball.add_file(file.path, file.mode) do |tarred_file|
        tarred_file.write file.read
      end
    end
def add_file(file)
      @tarball.add_file(file.path, file.mode) do |tarred_file|
        tarred_file.write file.read
      end
    end
Creates a new +GzippedTarball+. Provides the interface required by
 +AndFeathers::Directory#to_io+

 @param tarball [Gem::Package::TarWriter]


 Adds the given file to the tarball

 @param file [AndFeathers::File]