title: Import class only if it's available (e.g. UIPopOverControllerDelegate only on >= 3.2)
body: <p>I've got a class which is implementing the UIPopOverControllerDelegate:</p>
  
  <pre><code>#if ios_atleast_32
  @interface MyClass : UIViewController &lt;UIPopoverDelegate&gt;
  #elsif
  @interface MyClass : UIViewController
  #endif
  </code></pre>
  
  <p>Is it possible to make determine at runtime if the class is available and therefore should be used as delegate? The same for imports:</p>
  
  <pre><code>#if ios_4_available
  #import "MyClassWhichIsUsingIos4Stuff.h"
  #endif
  </code></pre>