Took AlterOrderWithRespectTo into account when optimizing migrations

Thanks Andrew Godwin for the review.

django/db/migrations/optimizer.py

@@ -21,6 +21,7 @@ class MigrationOptimizer(object):
             migrations.AlterModelTable,
             migrations.AlterUniqueTogether,
             migrations.AlterIndexTogether,
+            migrations.AlterOrderWithRespectTo,
         )
         self.field_level_operations = (
             migrations.AddField,
@@ -47,6 +48,11 @@ class MigrationOptimizer(object):
                 migrations.DeleteModel,
                 self.reduce_model_alter_delete,
             ),
+            (
+                migrations.AlterOrderWithRespectTo,
+                migrations.DeleteModel,
+                self.reduce_model_alter_delete,
+            ),
             (
                 migrations.CreateModel,
                 migrations.RenameModel,

tests/migrations/test_optimizer.py

@@ -93,20 +93,30 @@ class OptimizerTests(SimpleTestCase):
             ],
         )
 
-    def test_create_alter_delete_model(self):
+    def _test_create_alter_foo_delete_model(self, alter_foo):
         """
-        CreateModel, AlterModelTable, AlterUniqueTogether, and DeleteModel should collapse into nothing.
+        CreateModel, AlterModelTable, AlterUniqueTogether/AlterIndexTogether/
+        AlterOrderWithRespectTo, and DeleteModel should collapse into nothing.
         """
         self.assertOptimizesTo(
             [
                 migrations.CreateModel("Foo", [("name", models.CharField(max_length=255))]),
                 migrations.AlterModelTable("Foo", "woohoo"),
-                migrations.AlterUniqueTogether("Foo", [["a", "b"]]),
+                alter_foo,
                 migrations.DeleteModel("Foo"),
             ],
             [],
         )
 
+    def test_create_alter_unique_delete_model(self):
+        self._test_create_alter_foo_delete_model(migrations.AlterUniqueTogether("Foo", [["a", "b"]]))
+
+    def test_create_alter_index_delete_model(self):
+        self._test_create_alter_foo_delete_model(migrations.AlterIndexTogether("Foo", [["a", "b"]]))
+
+    def test_create_alter_owrt_delete_model(self):
+        self._test_create_alter_foo_delete_model(migrations.AlterOrderWithRespectTo("Foo", "a"))
+
     def test_optimize_through_create(self):
         """
         We should be able to optimize away create/delete through a create or delete