# File lib/backports/tools/std_lib.rb, line 41
      def extend_relative relative_dir="stdlib"
        loaded = Backports::StdLib::LoadedFeatures.new
        dir = File.expand_path(relative_dir, File.dirname(caller.first.split(/:\d/,2).first))
        Dir.entries(dir).
          map{|f| Regexp.last_match(1) if /^(.*)\.rb$/ =~ f}.
          compact.
          each do |f|
            path = File.expand_path(f, dir)
            if loaded.include?(f)
              require path
            else
              @extended_lib[f] << path
            end
          end
      end