title: Mongoose won't update new field after updating schema declaration
body: <p>I just noticed that when i update my schema definition and add a field, for instance "name: String" and then try to use </p>
  
  <pre><code>People.update( { _id: user_id }, { $set: { name: 'something' } } ) 
  </code></pre>
  
  <p>mongoose won't update my property.</p>
  
  <p>I keep getting nModified: 0 on the response.</p>
  
  <p>The only way i found to fix it, is to Drop the collection and then the new documents will work perfectly.</p>
  
  <p>Am i missing something? Does mongoose somehow "caches" the schema of a collection on mongodb itself and then needs a "drop" in order to "reload" the properties?</p>