def concat_enum(enum_enum)
      Enumerator.new do |yielder|
        enum_enum.each do |enum|
          enum.each { |i| yielder << i }
        end
      end
    end
def concat_enum(enum_enum)
      Enumerator.new do |yielder|
        enum_enum.each do |enum|
          enum.each { |i| yielder << i }
        end
      end
    end
Concatinates two enumerators
 @todo find a better home for this. Reopen Enumerable? or use the
    `Enumerating` gem: https://github.com/mdub/enumerating