message: Write invalid data when cloning to force an abort
  Otherwise it seems libgit2 isn't ready to handle premature eof? Unclear...
diff: @@ -2205,7 +2205,9 @@ fn failed_submodule_checkout() {
  let t = thread::spawn(move || {
  while !done2.load(Ordering::SeqCst) {
  - drop(listener.accept());
  + if let Ok((mut socket, _)) = listener.accept() {
  + drop(socket.write_all(b"foo\r\n"));
  + }
  }
  });
  