remove infinite loop in instanceOf

Source/Core/Core.js

@@ -45,12 +45,17 @@ var typeOf = this.typeOf = function(item){
 };
 
 var instanceOf = this.instanceOf = function(item, object){
+	var ctors = [];
 	if (item == null) return false;
 	var constructor = item.$constructor || item.constructor;
 	while (constructor){
+		if (ctors.contains(constructor)) break;
+		ctors.push(constructor);
+
 		if (constructor === object) return true;
 		constructor = constructor.parent;
 	}
+	ctors = null;
 	/*<ltIE8>*/
 	if (!item.hasOwnProperty) return false;
 	/*</ltIE8>*/

Specs/Core/Core.js

@@ -607,6 +607,38 @@ describe('instanceOf', function(){
 		expect(instanceOf(new X, Array)).to.equal(true);
 	});
 
+	it('should not go into infinite loop', function(){
+		// self reference case
+		var Foo = function Foo(){
+			var ctor = this.constructor;
+			ctor.parent = ctor;
+		};
+		expect(instanceOf(new Foo(), Foo)).to.equal(true);
+		expect(instanceOf(new Foo(), String)).to.equal(false);
+
+		// circular reference case
+		var A, B;
+		A = function(){this.init();};
+		B = function(){this.init();};
+
+		A.prototype.init = function(){
+			this.constructor = B;
+		};
+		A.prototype.parent = B;
+
+		B.prototype.init = function(){
+			this.constructor = A;
+		};
+		B.prototype.parent = A;
+
+		expect(instanceOf(new A(), B)).to.equal(true);
+		expect(instanceOf(new A(), A)).to.equal(true);
+		expect(instanceOf(new B(), B)).to.equal(true);
+		expect(instanceOf(new B(), A)).to.equal(true);
+
+		expect(instanceOf(new A(), String)).to.equal(false);
+	});
+
 	// todo(ibolmo)
 	var dit = typeof window != 'undefined' && window.Element && Element.set ? it : xit;
 	dit('should return true for Element instances', function(){