static MultiMap<S> allLoadedLibrariesPlusLoadingProgramIDs() {
  new MultiMap<S> mm;
  for (ClassLoader cl : allJavaXClassLoaders()) {
    S progID = (S) getOpt(cl, 'progID);
    L<File> files = cast getOpt(cl, 'files);
    for (File f : dropFirst(files))
      mm.put(DiskSnippetCache_fileToLibID(f), progID);
  }
  ret mm;
}