Fixed: CPImage -size returned internal object ref

Previously, CPImage -size returned a reference to the internal _size object, which allowed the caller to directly change _size. In Cocoa a copy of the size is returned.

This commit returns a copy of _size to ensure no unwanted side effects.

AppKit/CPImage.j

@@ -275,7 +275,7 @@ function CPAppKitImage(aFilename, aSize)
 */
 - (CGSize)size
 {
-    return _size;
+    return CGSizeMakeCopy(_size);
 }
 
 + (id)imageNamed:(CPString)aName