class WWW::Mechanize::File

def save_as(filename = nil)
  if filename.nil?
    filename = @filename
    number = 1
    while(::File.exists?(filename))
      filename = "#{@filename}.#{number}"
      number += 1
    end
  end
  ::File::open(filename, "wb") { |f|
    f.write body
  }
end