title: $resource on DELETE does not serialize data in json
body: <p>When using $resource with POST method (the item i want to delete on the server is of type "Todo")
  My java SpringREST back controller looks like :</p>
  
  <pre><code>/**
   * POST : delete an todo : /todos/DEL
   */
  @RequestMapping(value = "/DEL", method = RequestMethod.POST)
  public void deletePOST(@RequestBody Todo todo) {
      todoRepository.delete(todo);
  }
  </code></pre>
  
  <p>Angular code :</p>
  
  <pre><code> vm.deleteTodoRes2 = function deleteTodoRes2(todo) {
                  console.log(todo);
                  var url = REST_SERVER_URL + "/todos/DEL";
                  var urlParamDefaults = {};
                  var action = {
                      removeResource: {
                          method: 'POST',
                          headers: {
                              'Content-Type': 'application/json'
                          },
                          isArray: false,
                          transformRequest : function(data, headers) {
                              console.log("data");
                              console.log(data);
                              var out = angular.toJson(data);
                              console.log("out ");
                              console.log(out);
                              return  out;
                          }
                      }
                  };
                  var rest = $resource(url, urlParamDefaults, action);
                  // API : rest.&lt;method&gt; ( [param],
                  //                       if NON GET [entityData],
                  //                      [success(value, responseHeaders)], [error(httpResponse)] )
                  var param = {};
                  rest.removeResource(param, todo,  successCallback, errorCallback);
              };
  </code></pre>
  
  <p>It works perfectlt with POST,
  Now if i try changing the http method from POST to DELETE, it does not work anymore.</p>
  
  <p>Spring :</p>
  
  <pre><code> @RequestMapping(value = "/DEL", method = RequestMethod.DELETE)  &lt;&lt;&lt; only change in JAVA
  In JS
  
  var action = {  removeResource: { method: 'DELETE ', &lt;&lt;&lt; only change in JS
  </code></pre>
  
  <p>It does NOT WORK ,
  the console.log(data); => undefined
  It seems the Angular does NOT want to take my "toto" data and serialize it in json,
  why ?</p>