title: how can you find out if an NSObject has a certain property?
body: <p>Let's say in Apple API version 1.0, there is a class NSFoo with a property 'color'.  API 1.1 adds property 'size'.</p>
  
  <p>I want to know whether I can use the getter: myFoo.size</p>
  
  <p>[myFoo respondsToSelector:@selector(getSize)] doesn't work as expected.</p>
  
  <p>What's the correct way to find out if an object has a property?  Thanks!</p>