respect traditional: true option in $.ajax()

Forward the value of `traditional` option to $.param() in order to
activate flat parameter serialization for certain backends such as
Django.

Closes madrobby#484

src/ajax.js

@@ -152,7 +152,7 @@
 
   // serialize payload and append it to the URL for GET requests
   function serializeData(options) {
-    if (isObject(options.data)) options.data = $.param(options.data)
+    if (isObject(options.data)) options.data = $.param(options.data, options.traditional)
     if (options.data && (!options.type || options.type.toUpperCase() == 'GET'))
       options.url = appendQuery(options.url, options.data)
   }

test/ajax.html

@@ -407,6 +407,12 @@ <h1>Zepto Ajax unit tests</h1>
         t.assertEqual('hello=world&array[]=1&array[]=2&array[]=3&object[prop1]=val&object[prop2]=2', MockXHR.last.data)
       },
 
+      testDataOptionIsConvertedToSerializedTraditionalForm: function(t) {
+        $.ajax({ data: {hello: 'world', array: [1,2,3], object: { prop1: 'val', prop2: 2 } }, traditional: true })
+        MockXHR.last.data = decodeURIComponent(MockXHR.last.data)
+        t.assertEqual('hello=world&array=1&array=2&array=3&object=[object+Object]', MockXHR.last.data)
+      },
+
       testDataIsAppendedToGETURL: function(t) {
         $.ajax({ url:'test.html', data:'foo=bar' })
         t.assertEqual('test.html?foo=bar', MockXHR.last.url)