Attempt to fix focus transfer issue between Display and AWT components in JDK 7:

- Instead of grabbing focus directly to our window, we call requestFocus on the Canvas component. This will clear focus from any other AWT component.
- When the parent Canvas gets focus, we detect it in update and that's when we grab focus to our window. We can't use a listener, setFocus must be called in our thread.
- Alt-tabbing out/in also works because focus goes to the Canvas. The above check will trigger again and our window will be refocused.