A child entity that was temporarily added and then deleted is still inserted

[sashakboo]

A child entity that was temporarily added and then deleted will still be inserted if the parent entity is reattached to a new session.

Book book = null;
using (var s = OpenSession())
using (var tr = s.BeginTransaction())
{
  book = new Book { Id = 1};
  book.Words = new List<Word> { new Word { Id = 1, Parent = book } };
  s.Save(book);
  tr.Commit();
}

// Adding temporary child on detached entity.
Word word = new Word { Id = 2, Parent = book };
book.Words.Add(word);

using (var s = OpenSession())
using (var tr = s.BeginTransaction())
{
  // Attach entity to new session and remove temporary child.
  s.Update(book);
  book.Words.Remove(word);
  // This produces insert command for removed child.
  tr.Commit();
}

Maybe it's a duplicate of #2028

Tests here:
#3666