title: Backbone model.save() is sending PUT instead of POST
body: <p>I call save using this:</p>
  
  <pre><code>console.log(this.model.isNew());
  console.log(this.model);
  
  this.model.save({}, {
      success: function (model, response, options) {
          console.log(response);
      },
      error: function (model, xhr, options) {
          console.log(xhr.result.Errors);
      }   
  });
  </code></pre>
  
  <p>The <code>isNew()</code> returns false. But the output of <code>this.model</code> has an ID of 0. (this.model.id is 0 as well)</p>
  
  <p>My url is <code>url: ROOTAREA + "/Expenses/Entry/",</code> </p>
  
  <p>Updating works fine, and uses PUT as expected.</p>
  
  <p>Edit : here's part of my model:</p>
  
  <pre><code>   defaults: function () {
          return {
              DocumentDate: "",
              JobNo_: "",
              PhaseCode: "",
              WorkTypeCode: "",
              Description: "",
              Quantity: 0,
              UnitCost: 0,
              ExpenseCurrencyCode: "",
              ReimbursementCurrencyCode: "",
              UnitofMeasureCode: "DIEM",
              LineNo_: 0
          };
      },
      idAttribute: "LineNo_",
  </code></pre>