Merge branch 'lt/dir-cleanup'

* lt/dir-cleanup:
  Make index preloading check the whole path to the file
  Export thread-safe version of 'has_symlink_leading_path()'
  Prepare symlink caching for thread-safety
  Avoid using 'lstat()' to figure out directories
  Avoid doing extra 'lstat()'s for d_type if we have an up-to-date cache entry
  Simplify read_directory[_recursive]() arguments
  Add 'fill_directory()' helper function for directory traversal