New way to fix BUG#19243 "wrong LAST_INSERT_ID() after ON DUPLICATE KEY UPDATE".

This bug report was two problems:
1) LAST_INSERT_ID() returns a value which does not exist in the table
2) the reporter would want it to return the autoinc id of the updated
row.
1) is a real bug, 2) is a feature request.
In July I implemented 2) in 5.1 (which automatically fixes 1).
This has not yet been documented or released, so is changeable.
Precisely, recently Paul and a user found an easy workaround to give
2), which works in 4.1-5.0-5.1. So I can revert my code for 2),
because it's not needed, that's what I do here;
we forget about 2) (we will document the workaround).
But when I revert my code for 2), 1) comes back. We solve 1) by saying
that if INSERT ON DUPLICATE KEY UPDATE updates a row, it's like a
regular UPDATE: LAST_INSERT_ID() should not be affected (instead of
returning a non-existent value).
So note: no behaviour change compared to the last released 5.1; just
a bugfix for 1).

mysql-test/r/innodb_mysql.result

@@ -432,22 +432,44 @@ ifnull( c,
 0 ) + 1;
 select last_insert_id();
 last_insert_id()
-1
+2
+select last_insert_id(0);
+last_insert_id(0)
+0
+insert into t2 ( a ) values ( 6 ) on duplicate key update c =
+ifnull( c,
+0 ) + 1;
+select last_insert_id();
+last_insert_id()
+0
 select * from t2;
 k	a	c
-1	6	1
+1	6	2
 2	7	NULL
 insert ignore into t2 values (null,6,1),(10,8,1);
 select last_insert_id();
 last_insert_id()
-1
+0
 insert ignore into t2 values (null,6,1),(null,8,1),(null,15,1),(null,20,1);
 select last_insert_id();
 last_insert_id()
 11
 select * from t2;
 k	a	c
-1	6	1
+1	6	2
+2	7	NULL
+10	8	1
+11	15	1
+12	20	1
+insert into t2 ( a ) values ( 6 ) on duplicate key update c =
+ifnull( c,
+0 ) + 1, k=last_insert_id(k);
+select last_insert_id();
+last_insert_id()
+1
+select * from t2;
+k	a	c
+1	6	3
 2	7	NULL
 10	8	1
 11	15	1