Fix noderequest uniqueness by adding back RunSQL calls

Note: this is a temporary commit to pass CI only. The change
      in this commit will be included in another PR or commit
      that should aggregate all RunSQL calls for indexes.

osf/migrations/0003_aggregated_runsql_calls.py

@@ -0,0 +1,25 @@
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('osf', '0002_adminlogentry'),
+    ]
+
+    operations = [
+        migrations.RunSQL(
+            [
+                """
+                CREATE UNIQUE INDEX osf_noderequest_target_creator_non_accepted ON osf_noderequest (target_id, creator_id)
+                WHERE machine_state != 'accepted';
+                """
+            ], [
+                """
+                DROP INDEX IF EXISTS osf_noderequest_target_creator_non_accepted RESTRICT;
+                """
+            ]
+        ),
+    ]