Avoid creating a closure here
DisplayUtil.hitTestTouch
DisplayUtil.isAncestor
GameObjectRef.displayOn()

This simplifies the GameObjectContainer interface, and is easier to
read.

This regex substitution will convert most uses of the old form to the
new one:

s/addObject\(([\w\.]*?), ([\w\.]*?)\)/addObject($1).displayOn($2)/g
Revert "GameObjectRef.displayOn()"

This reverts commit 5537a53a059f06fc6ec8db5ffe673178bbc9d5c4.

This change caused GameObjects to be attached to the displayList
*after* their added() function was called, which is not
desirable.
Collision utils moved to aspire