// returns true if file was changed
sbool cleanFluidTextFile(File f) {
  new CleanFluidTextFile cleaner;
  {
    temp Reader reader = utf8reader(f);
    cleaner.reader = reader;
    cleaner.read();
  }
  new StringWriter writer;
  cleaner.writer = writer;
  cleaner.write();
  S out = str(writer);
  ret saveTextFileIfDifferent(f, out);
}