Tree: Cannot drop item into folder if it is adjacent to the source folder

[ptwobrussell]

I just noticed while working up some content with the dnd Tree that you cannot drop an item into the folder directly below it if the item is initially adjacent to it. You can however, drag the item somewhere else that'll accept it, and then move it back to the folder and drop it.

You can view this from the night test (​http://archive.dojotoolkit.org/nightly/dojotoolkit/dijit/tests/tree/test_Tree_DnD.html on 4 Mar) by loading the page and trying to drag the Orange directly into the Vegetables folder. It won't work. But...drag it down to Cereals and then back up to Vegetables and it's ok for the drop.

This is actually in 1.1b2, I believe, but that's not an option, so I'll pick 1.1b1 for version.

[bill]

(In [13125]) Fix problem where drop target validity was based on the previous node that was hovered over, not the node currently being hovered over. Also stopped using "n" to mean two different things (in the same function). Fixes #6080. !strict