# File setup.rb, line 1256
  def ruby_extentions(dir)
    Dir.open(dir) {|d|
      ents = d.select {|fname| /\.#{::Config::CONFIG['DLEXT']}\z/ =~ fname }
      if ents.empty?
        setup_rb_error "no ruby extention exists: 'ruby #{$0} setup' first"
      end
      return ents
    }
  end