Additional test for Bugs#20392: INSERT_ID session variable has weird value

sys_var_insert_id returned LAST_INSERT_ID instead of INSERT_ID,
as Guilhem suggested.

mysql-test/r/variables.result

@@ -429,6 +429,16 @@ set session insert_id=20;
 select @@session.insert_id;
 @@session.insert_id
 20
+set session last_insert_id=100;
+select @@session.insert_id;
+@@session.insert_id
+20
+select @@session.last_insert_id;
+@@session.last_insert_id
+100
+select @@session.insert_id;
+@@session.insert_id
+20
 set @@session.insert_id=@save_insert_id;
 select @@session.insert_id;
 @@session.insert_id

mysql-test/t/variables.test

@@ -308,6 +308,12 @@ select @@session.insert_id;
 set @save_insert_id=@@session.insert_id;
 set session insert_id=20;
 select @@session.insert_id;
+
+set session last_insert_id=100;
+select @@session.insert_id;
+select @@session.last_insert_id;
+select @@session.insert_id;
+
 set @@session.insert_id=@save_insert_id;
 select @@session.insert_id;