# File setup.rb, line 442
  def mkdir_p(dirname, prefix = nil)
    dirname = prefix + File.expand_path(dirname) if prefix
    $stderr.puts "mkdir -p #{dirname}" if verbose?
    return if no_harm?

    # does not check '/'... it's too abnormal case
    dirs = File.expand_path(dirname).split(%r<(?=/)>)
    if /\A[a-z]:\z/i =~ dirs[0]
      disk = dirs.shift
      dirs[0] = disk + dirs[0]
    end
    dirs.each_index do |idx|
      path = dirs[0..idx].join('')
      unless File.dir?(path)
        Dir.mkdir path
        File.chmod(0755,path)
      end
    end
  end