filename_escape (OpenID::Store::Filesystem)

    # File lib/openid/store/filesystem.rb, line 232
          def filename_escape(s)
            s = '' if s.nil?
            filename_chunks = []
            s.split('').each do |c|
              if @@FILENAME_ALLOWED.index(c)
                filename_chunks << c
              else
                filename_chunks << sprintf("_%02X", c[0])
              end
            end
            filename_chunks.join("")
          end