filter_out_descendants

# File activesupport/lib/active_support/evented_file_update_checker.rb, line 208
        def filter_out_descendants(dirs)
          return dirs if dirs.length < 2

          dirs_sorted_by_nparts = dirs.sort_by { |dir| dir.each_filename.to_a.length }
          descendants = []

          until dirs_sorted_by_nparts.empty?
            dir = dirs_sorted_by_nparts.shift

            dirs_sorted_by_nparts.reject! do |possible_descendant|
              ascendant_of?(dir, possible_descendant) && descendants << possible_descendant
            end
          end

          # Array#- preserves order.
          dirs - descendants
        end