Make sure to return the current version of entity from tree.intersects

Since d5e427289, the tree head graph will not update if only tags have
changed - it requires an addition, deletion, or geometry change.

This makes the tree a little more efficient, but we do need to make
sure to return the current entities to the caller.

modules/core/tree.js

@@ -98,7 +98,7 @@ export function coreTree(head) {
         }
 
         return rtree.search(extent.bbox())
-            .map(function(bbox) { return head.entity(bbox.id); });
+            .map(function(bbox) { return graph.entity(bbox.id); });
     };