Tree: drop between has strange placement for TreeStoreModel w/multiple childrenAttrs

[bill]

Using test_Tree_Dnd.html, and dragging any item and trying to drop it (for example) before or after the Vegetables category will put it under Foods, before any of the categories.

[bill]

The problem happens in TreeStoreModel.pasteItem() when it tries to get the children of the "Foods" parent node via:

var childItems = store.getValues(newParentItem, parentAttr).slice();

It's failing because of the line:

parentAttr = this.childrenAttrs[0];	// name of "children" attr in parent item

The problem is that childrenAttrs specifies multiple attributes (item and children), due to an ill-conceived feature added in #4528, and it's only checking items[], not children[].

This will all go away in 2.0, along with TreeStoreModel.js itself, so it's not worth fixing this bug.