fix serious performance problem of Animate.

this is a serious bug, it cause massive cpu consume.
if we have 1000 animate in active scene, this pr can raise 5% performance globally, raise about 70% performance locally of Animate!!!!!!!!!!!! .
because it have massive calls cocos2d::Vector constructor and de-constructor. 
Vector's constructor will also call "addRefForAllObjects"(for loop)!!!!!


This problem is very, very serious,  and still has many similar errors in cocos2d-x.

we must use "auto&" sometimes, especially in update per frame. 
I wrote a test case like this
```c++
class Test
{
public:
    Test()
    {
        printf("Test\n");
    }
    
    void func()
    {
        printf("func");
    }
};

class ReturnReference
{
public:
    Test& getTest()
    {
        test = new Test;
        return *test;
    }
    
    Test *test;
};

int main(int argc, const char * argv[]) {
    
    ReturnReference returnReference;
    
    auto test = returnReference.getTest();
    test.func();
    
    // insert code here...
    std::cout << "Hello, World!\n";
    return 0;
}
```

Test() was only invoked once. It means `auto test = returnReference.getTest();` doesn't create a new Test. So why need to use `auto&`?