class Gem::Commands::SetupCommand

def remove_old_lib_files lib_dir
  rubygems_dir = File.join lib_dir, 'rubygems'
  lib_files = rb_files_in 'lib/rubygems'
  old_lib_files = rb_files_in rubygems_dir
  to_remove = old_lib_files - lib_files
  to_remove.delete_if do |file|
    file.start_with? 'defaults'
  end
  Dir.chdir rubygems_dir do
    to_remove.each do |file|
      FileUtils.rm_f file
      warn "unable to remove old file #{file} please remove it by hand" if
        File.exist? file
    end
  end
end