Add default values for on* properties

Author: Abilash Badri

test/initialization_test.js

@@ -62,4 +62,4 @@ QUnit.test( "onreadystatechange is null", function( assert ) {
 
 QUnit.test( "ontimeout is null", function( assert ) {
   assert.equal( xhr.ontimeout, null );
-});
+});