rem: int append_dot = (length == FILESYSTEM_PREFIX_LEN (path));
add: bool append_dot = (length == FILE_SYSTEM_PREFIX_LEN (path));
context: dir_name (char const *path){  size_t length = dir_len (path);  int append_dot = (length == FILESYSTEM_PREFIX_LEN (path));  char *newpath = xmalloc (length + append_dot + 1);  memcpy (newpath, path, length);  if (append_dot)    newpath[length++] = '.';  newpath[length] = 0;  return newpath;}