fix(Angular): make Date comparison in equals() NaN-aware

Make angular.equals() Date comparison NaN-aware to prevent infinite digest errors when a dealy watched
date has an invalid value.

Closes #8650
Closes #8715

Author: SekibOmazic

src/Angular.js

@@ -911,7 +911,8 @@ function equals(o1, o2) {
           return true;
         }
       } else if (isDate(o1)) {
-        return isDate(o2) && o1.getTime() == o2.getTime();
+        if (!isDate(o2)) return false;
+        return (isNaN(o1.getTime()) && isNaN(o2.getTime())) || (o1.getTime() === o2.getTime());
       } else if (isRegExp(o1) && isRegExp(o2)) {
         return o1.toString() == o2.toString();
       } else {

test/AngularSpec.js

@@ -366,6 +366,11 @@ describe('angular', function() {
       expect(equals(new Date(0), new Date(1))).toBe(false);
       expect(equals(new Date(0), 0)).toBe(false);
       expect(equals(0, new Date(0))).toBe(false);
+
+      expect(equals(new Date(undefined), new Date(undefined))).toBe(true);
+      expect(equals(new Date(undefined), new Date(0))).toBe(false);
+      expect(equals(new Date(undefined), new Date(null))).toBe(false);
+      expect(equals(new Date(undefined), new Date('wrong'))).toBe(true);
     });
 
     it('should correctly test for keys that are present on Object.prototype', function() {