Fixing same-origin AJAX requests

jQuery sends multiple values for the `X-REQUESTED-WITH` header if it has already been set, even when the value is the same. This means that same-origin requests would send `X-REQUESTED-WITH: XMLHttpRequest, XMLHttpRequest` which isn't detected as AJAX by Laravel/Symphony.

To fix this issue while retaining the crossDomain usage of framework.js, I've used `crossDomain: false` to trick jQuery into sending the header anyways on cross-origin requests. This is still changeable by the user in the `ajaxSetup` event.

modules/system/assets/js/framework.js

@@ -65,7 +65,6 @@ if (window.jQuery.request !== undefined) {
         }
 
         var requestHeaders = {
-            'X-REQUESTED-WITH': 'XMLHttpRequest',
             'X-OCTOBER-REQUEST-HANDLER': handler,
             'X-OCTOBER-REQUEST-PARTIALS': this.extractPartials(options.update)
         }
@@ -76,6 +75,7 @@ if (window.jQuery.request !== undefined) {
 
         var requestOptions = {
             url: window.location.href,
+            crossDomain: false,
             context: context,
             headers: requestHeaders,
             success: function(data, textStatus, jqXHR) {