Fix for bug #11896 "Partial locking in case of recursive trigger definitions".

If we are in stored function or trigger we should ensure that we won't change
table that is already used by calling statement (this can damage table or
easily cause infinite loops). Particularly this means that recursive triggers
should be disallowed.

mysql-test/r/sp-error.result

@@ -299,6 +299,36 @@ lock tables t1 read, mysql.proc read|
 unlock tables|
 lock tables mysql.proc write|
 unlock tables|
+drop function if exists f1|
+create function f1(i int) returns int
+begin
+insert into t1 (val) values (i);
+return 0;
+end|
+select val, f1(val) from t1|
+ERROR HY000: Can't update table 't1' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
+select val, f1(val) from t1 as tab|
+ERROR HY000: Can't update table 't1' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
+select * from t1|
+val	x
+42	3.1
+19	1.2
+update t1 set val= f1(val)|
+ERROR HY000: Can't update table 't1' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
+select * from t1|
+val	x
+42	3.1
+19	1.2
+select f1(17)|
+f1(17)
+0
+select * from t1|
+val	x
+42	3.1
+19	1.2
+17	NULL
+delete from t1 where val= 17|
+drop function f1|
 create procedure bug1965()
 begin
 declare c cursor for select val from t1 order by valname;