def find_in_cache(filename)
    Gem.path.each do |path|
      this_path = File.join(path, "cache", filename)
      return this_path if File.exist? this_path
    end

    return nil
  end
#

Find cached filename in Gem.path. Returns nil if the file cannot be found.

--
TODO: see comments in get_path() about general service.