message: cmake: add option to workaround issue observed with old CMake
  CMake message contains this: "Invalid escape sequence \"
diff: @@ -156,11 +156,13 @@ function(ocv_download)
  TIMEOUT 600
  STATUS status
  LOG __log)
  + if(NOT OPENCV_SKIP_FILE_DOWNLOAD_DUMP) # workaround problem with old CMake versions: "Invalid escape sequence"
  string(LENGTH "${__log}" __log_length)
  if(__log_length LESS 65536)
  string(REPLACE "\n" "\n# " __log "${__log}")
  ocv_download_log("# ${__log}\n")
  endif()
  + endif()
  if(NOT status EQUAL 0)
  set(msg_level FATAL_ERROR)
  if(DEFINED DL_STATUS)
  