fix(angular.equals): consistently compare undefined object props

previously:

a = {};
b = {x:undefined};
angular.equals(a, b) == angular.equals(b, a) // returns false.

both should return false because these objects are not equal.

unlike in implemented in angular#1695 the comparison should be stricter
and return false not true. if we need to relax this in the future
we can always do so.

Closes angular#1648

src/Angular.js

@@ -620,16 +620,23 @@ function equals(o1, o2) {
       } else {
         if (isScope(o1) || isScope(o2) || isWindow(o1) || isWindow(o2)) return false;
         keySet = {};
+        length = 0;
         for(key in o1) {
-          if (key.charAt(0) !== '$' && !isFunction(o1[key]) && !equals(o1[key], o2[key])) {
-            return false;
-          }
+          if (key.charAt(0) === '$') continue;
+
+          if (!isFunction(o1[key]) && !equals(o1[key], o2[key])) return false;
+
+          length++;
           keySet[key] = true;
         }
         for(key in o2) {
-          if (!keySet[key] && key.charAt(0) !== '$' && !isFunction(o2[key])) return false;
+          if (key.charAt(0) === '$') {
+            continue;
+          }
+          if (!keySet[key] && !isFunction(o2[key])) return false;
+          length--;
         }
-        return true;
+        return length === 0;
       }
     }
   }

test/AngularSpec.js

@@ -126,6 +126,14 @@ describe('angular', function() {
       expect(equals(['misko'], ['misko', 'adam'])).toEqual(false);
     });
 
+    it('should ignore undefined member variables', function() {
+      var obj1 = {name: 'misko'},
+          obj2 = {name: 'misko', undefinedvar: undefined};
+
+      expect(equals(obj1, obj2)).toBe(false);
+      expect(equals(obj2, obj1)).toBe(false);
+    });
+
     it('should ignore $ member variables', function() {
       expect(equals({name:'misko', $id:1}, {name:'misko', $id:2})).toEqual(true);
       expect(equals({name:'misko'}, {name:'misko', $id:2})).toEqual(true);