add DijitRegistry#getParent

pls. add DijitRegistry#getParent for compatibility with dijit._KeyNavContainer

this is the code in dijit._KeyNavContainer

```
		childSelector: function(/*DOMNode*/ node){
			// Implement _KeyNavMixin.childSelector, to identify focusable child nodes.
			// If we allowed a dojo/query dependency from this module this could more simply be a string "> *"
			// instead of this function.

			var node = registry.byNode(node);
			return node && node.getParent() == this;
		}
```

Grid is received from registry, but it doesn't provide getParent(). Any _WidgetBase descendant would provide getParent().