title: MongoDB atomic "findOrCreate": findOne, insert if nonexistent, but do not update
body: <p>as the title says, I want to perform a find (one) for a document, by _id, and if doesn't exist, have it created, then whether it was found or was created, have it returned in the callback.</p>
  
  <p>I don't want to update it if it exists, as I've read findAndModify does. I have seen many other questions on Stackoverflow regarding this but again, don't wish to update anything.</p>
  
  <p>I am unsure if by creating (of not existing), THAT is actually the update everyone is talking about, it's all so confuzzling :(</p>