Mark null and undefined as undetectable, and use it to handle abstract equality comparison in the g…

test/mjsunit/typeof.js

 // Copyright 2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 17 matching lines @@
 // The type of a regular expression should be 'object', including in
 // the context of string equality comparisons.
 
 var r = new RegExp;
 assertEquals('object', typeof r);
 assertTrue(typeof r == 'object');
 assertFalse(typeof r == 'function');
 
 function test(x, y) { return x == y; }
 assertTrue(test('object', typeof r));
+
+assertFalse(typeof null == "undefined");