title: How to cancel an animation for a specific context and animationID?
body: <p>I have an animation which I kick off like this:</p>
  
  <pre><code>[UIView beginAnimations:@"doThis" context:self];
  [UIView setAnimationDuration:1.5f];
  [UIView setAnimationDelay:2.5f];
  </code></pre>
  
  <p>Now, the problem is that this animation is told to start in 2.5 seconds. But in the meantime, something may happen and I don't want the animation anymore. However, CA will just animate that thing after 2.5 seconds, no matter what happens. How could I say "no, thank you, don't animate"?</p>
  
  <p>I have other animations going on in different context and animationID, so I don't want to just remove all animations from the app. What's the most clean way of achieving this? Just running another nonsense-animation with same context and animationID and old targets?</p>