Fix change summary calculation after restoring

We can't rely on identity equality here due to how
restoring works, and don't want to anyway -- the summary
should ignore net-no-op tag changes.

Fixes #1915.

js/id/core/difference.js

@@ -118,8 +118,8 @@ iD.Difference = function(base, head) {
                 addEntity(change.base, base, 'deleted');
 
             } else if (change.base && change.head) { // modified vertex
-                var moved    = change.base.loc  !== change.head.loc,
-                    retagged = change.base.tags !== change.head.tags;
+                var moved    = !_.isEqual(change.base.loc,  change.head.loc),
+                    retagged = !_.isEqual(change.base.tags, change.head.tags);
 
                 if (moved) {
                     addParents(change.head);

test/spec/core/difference.js

@@ -265,6 +265,18 @@ describe("iD.Difference", function () {
             }]);
         });
 
+        it("does not report a vertex as modified when it is moved and has no-op tag changes", function() {
+            var vertex = base.entity('b').update({tags: {}, loc: [1, 2]}),
+                head = base.replace(vertex),
+                diff = iD.Difference(base, head);
+
+            expect(diff.summary()).to.eql([{
+                changeType: 'modified',
+                entity: head.entity('-'),
+                graph: head
+            }]);
+        });
+
         it("reports a vertex as deleted when it had tags", function() {
             var vertex = base.entity('v'),
                 head = base.remove(vertex),