Fix PGraphicsJava2D.copy() when src is of same class

[thobbs]

Using copy() a PGraphicsJava2D with a src that is also PGraphicsJava2D will produce the following error:

class sun.java2d.SunGraphics2D cannot be cast to class java.awt.Image

This is due to PGraphicsJava2D.native() returning g2 (a PGraphicsJava2D instance) rather than a java.awt.Image instance, which is what the cast here expects.

I've added specific handling for src being PGraphicsJava2D, as well as general handling of other non-Image results from src.getNative(). I built and tested this solution locally.

[thobbs]

Friendly bump after one year - any chance this could be fixed?