fix(angular.equals): do not match keys defined in the prototype chain

Merely testing for object[key] will give incorrect results on keys
defined in Object.prototype.
Note: IE8 is generally broken in this regard since `for...in` never returns
certain property keys even if they are defined directly on the object.

See #2141 - partially merges this PR

src/Angular.js

@@ -2,6 +2,16 @@
 
 ////////////////////////////////////
 
+/**
+ * hasOwnProperty may be overriden by a property of the same name, or entirely
+ * absent from an object that does not inherit Object.prototype; this copy is
+ * used instead
+ */
+var hasOwnPropertyFn = Object.prototype.hasOwnProperty;
+var hasOwnPropertyLocal = function(obj, key) {
+  return hasOwnPropertyFn.call(obj, key);
+};
+
 /**
  * @ngdoc function
  * @name angular.lowercase
@@ -685,7 +695,7 @@ function equals(o1, o2) {
           keySet[key] = true;
         }
         for(key in o2) {
-          if (!keySet[key] &&
+          if (!keySet.hasOwnProperty(key) &&
               key.charAt(0) !== '$' &&
               o2[key] !== undefined &&
               !isFunction(o2[key])) return false;

test/AngularSpec.js

@@ -270,6 +270,14 @@ describe('angular', function() {
       expect(equals(new Date(0), 0)).toBe(false);
       expect(equals(0, new Date(0))).toBe(false);
     });
+
+    it('should correctly test for keys that are present on Object.prototype', function() {
+      // MS IE8 just doesn't work for this kind of thing, since "for ... in" doesn't return
+      // things like hasOwnProperty even if it is explicitly defined on the actual object!
+      if (msie<=8) return;
+      expect(equals({}, {hasOwnProperty: 1})).toBe(false);
+      expect(equals({}, {toString: null})).toBe(false);
+    });
   });
 
   describe('size', function() {