title: Mongoose schema: 'unique' not being respected
body: <p>I'm trying to use Mongoose with this schema</p>
  
  <pre><code>var RestoSchema = new Schema({
      "qname"          : {type: String, required: true, unique: true},
      ...
  });
  </code></pre>
  
  <p>The problem is that this still permits new entries to the database to be created with an existing <code>qname</code>. From what i can see below the index has been created, but without any demonstrable impact when I use the <code>.save</code> method. What am I misunderstanding?</p>
  
  <pre><code>&gt; db.restos.getIndexes()
  [
      {
          "v" : 1,
          "key" : {
              "_id" : 1
          },
          "ns" : "af.restos",
          "name" : "_id_"
      },
      {
          "v" : 1,
          "key" : {
              "qname" : 1
          },
          "ns" : "af.restos",
          "name" : "qname_1",
          "background" : true,
          "safe" : null
      }
  ]
  </code></pre>