* adding diagnostic/user index

db/manifest

@@ -232,4 +232,5 @@ recurly.sql
 add_track_resource_id.sql
 user_genres.sql
 user_online.sql
-icecast_source_changes.sql
+icecast_source_changes.sql
+diagnostics_user_id_index.sql

db/up/diagnostics_user_id_index.sql

@@ -0,0 +1 @@
+CREATE INDEX diagnostics_user_id ON diagnostics USING btree(user_id);