# File lib/rails-installer.rb, line 554
  def sha1_hash_directory_tree(directory, prefix='', hash={})
    Dir.entries(directory).each do |file|
      next if file =~ /^\./
      pathname = File.join(directory,file)
      if File.directory?(pathname)
        sha1_hash_directory_tree(pathname, File.join(prefix,file), hash)
      else
        hash[File.join(prefix,file)] = Digest::SHA1.hexdigest(File.read(pathname))
      end
    end
    
    hash
  end