message: core: dump neighbour cache directories (from old OpenCV versions)
  use '3.4.x' cache name for current maintenance series (there are no serious changes between releases)
  message is shown only once during creation of new cache directory
  use OPENCV_CACHE_SHOW_CLEANUP_MESSAGE=0 to hide this warning
diff: @@ -469,7 +469,32 @@ cv::String getCacheDirectory(const char* sub_directory_name, const char* configu
  {
  if (utils::fs::isDirectory(default_cache_path))
  {
  - default_cache_path = utils::fs::join(default_cache_path, utils::fs::join("opencv", CV_VERSION));
  + cv::String default_cache_path_base = utils::fs::join(default_cache_path, "opencv");
  + default_cache_path = utils::fs::join(default_cache_path_base, "3.4.x" CV_VERSION_STATUS);
  + if (utils::getConfigurationParameterBool("OPENCV_CACHE_SHOW_CLEANUP_MESSAGE", true)
  + && !utils::fs::isDirectory(default_cache_path))
  + {
  + std::vector<cv::String> existedCacheDirs;
  + try
  + {
  + utils::fs::glob_relative(default_cache_path_base, "*", existedCacheDirs, false, true);
  + }
  + catch (...)
  + {
  + // ignore
  + }
  + if (!existedCacheDirs.empty())
  + {
  + CV_LOG_WARNING(NULL, "Creating new OpenCV cache directory: " << default_cache_path);
  + CV_LOG_WARNING(NULL, "There are several neighbour directories, probably created by old OpenCV versions.");
  + CV_LOG_WARNING(NULL, "Feel free to cleanup these unused directories:");
  + for (size_t i = 0; i < existedCacheDirs.size(); i++)
  + {
  + CV_LOG_WARNING(NULL, " - " << existedCacheDirs[i]);
  + }
  + CV_LOG_WARNING(NULL, "Note: This message is showed only once.");
  + }
  + }
  if (sub_directory_name && sub_directory_name[0] != '\0')
  default_cache_path = utils::fs::join(default_cache_path, cv::String(sub_directory_name) + native_separator);
  if (!utils::fs::createDirectories(default_cache_path))
  