title: NSSet containsObject Not Working?
body: <p>I am trying to check if the annotation exists before adding it to array. 
  I can't figure out why [visibleAnnotations containsObject:annotation] always returns False.   </p>
  
  <pre><code>MKMapRect mRect = self.locationView.visibleMapRect;
  NSSet *visibleAnnotations =[self.locationView annotationsInMapRect:mRect];
  NSLog(@"Annotation in Rect %@",visibleAnnotations);
  
  for(NSArray * obj in JSON){
                  coordinates.latitude=[[obj valueForKey:@"Latitude"] doubleValue];
                  coordinates.longitude=[[obj valueForKey:@"Longitude"] doubleValue];
                  NSString *title=[NSString stringWithFormat:@"%@",[obj valueForKey:@"DeviceId"]];
                  MapAnnotation *annotation = [[MapAnnotation alloc] initWithTitle:title andCoordinate:coordinates] ;
  
                  NSLog(@"New Annotation %@",annotation);
  
                  if ([visibleAnnotations containsObject:annotation ]) {
                      //[addPins addObject:annotation];
                      NSLog(@"Contains obj");
                  }
                  [addPins addObject:annotation];
                  [annotation release];
              }
  </code></pre>
  
  <p>Zoomed to only show 1 annotation.</p>
  
  <pre><code> Annotation in Rect {(&lt;MapAnnotation: 0x1cd80720&gt;)}
   New Annotation &lt;MapAnnotation: 0x1cd79410&gt;
  </code></pre>
  
  <p>Thanks</p>