Fix Ox.Request.cancel(fn) (fixes #2932)

arguments[0] === req inside the forEach callback, so previously this
would throw

    TypeError: arguments[0] is not a function

source/UI/js/Core/Request.js

@@ -48,8 +48,9 @@ Ox.Request = (function() {
                 requests = {};
             } else if (Ox.isFunction(arguments[0])) {
                 // cancel with function
+                var fn = arguments[0];
                 Ox.forEach(requests, function(req, id) {
-                    if (arguments[0](req)) {
+                    if (fn(req)) {
                         delete requests[id];
                     }
                 });