Dynamically set debug flag for session only

- avoid restart
- keep all in one file
- fix --check-testcase

mysql-test/r/error_simulation.result

@@ -13,6 +13,7 @@ INSERT INTO t1 VALUES
 ('AAAAAAAAAH','AAAAAAAAAH'), ('AAAAAAAAAI','AAAAAAAAAI'),
 ('AAAAAAAAAJ','AAAAAAAAAJ'), ('AAAAAAAAAK','AAAAAAAAAK');
 set tmp_table_size=1024;
+set session debug="d,raise_error";
 SELECT MAX(a) FROM t1 GROUP BY a,b;
 ERROR 23000: Can't write; duplicate key in table 'tmp_table'
 set tmp_table_size=default;

mysql-test/t/error_simulation-master.opt

---loose-debug=d,raise_error

mysql-test/t/error_simulation.test

@@ -21,10 +21,15 @@ INSERT INTO t1 VALUES
 
 set tmp_table_size=1024;
 
+# Set debug flag so an error is returned when
+# tmp table in query is converted from heap to myisam
+set session debug="d,raise_error";
+
 --replace_regex /in table '[^']+'/in table 'tmp_table'/
 --error ER_DUP_KEY
 SELECT MAX(a) FROM t1 GROUP BY a,b;
 
 set tmp_table_size=default;
-
 DROP TABLE t1;
+
+