title: NSButton with clickable image and text
body: <p>I've created an NSButton (see code below).  The button displays the way I want (borderless, with image above text).  If I click the text portion of the button the button will press down and call it's action.  If I click the image portion of the button then absolutely nothing happens.  How can I make the image portion of the NSButton clickable?  I'm sure I can subclass the NSButtonCell to make this work, but I don't understand why that would be necessary.</p>
  
  <pre><code>NSButton *button = [[NSButton alloc] initWithFrame:NSZeroRect];
  [button setBezelStyle:NSRegularSquareBezelStyle];
  [button setBordered:YES];
  [button setImagePosition:NSImageAbove];
  [button setButtonType:NSMomentaryChangeButton];
  [button setImage:[NSImage imageNamed:@"myImage"]];
  [button setTitle:@"Button Title"];
  [button setTarget:self];
  [button setAction:@selector(buttonAction:)];
  </code></pre>