AUI-1320 A User can add duplicate child nodes

Hey Jon. This one is a little wierd. First, AUI-950 only ever affected 2.0.x and 2.5.x. We should not have fixed it on master, master-deprecated but we did.  Further, I found that applying AUI-1014 from Nate's merge with master fixes both AUI-950 and AUI-1014. And since AUI-950 causes AUI-1320, we should be able to safely revert this one. Its a bit confusing but if you have any questions tomorrow, let me know.