Port r100 from branches/5.0 to trunk.

mysql-test/innodb_unsafe_binlog-master.opt

+--innodb_locks_unsafe_for_binlog=true

mysql-test/innodb_unsafe_binlog.result

+drop table if exists t1,t2;
+create table t1 (id int not null, f_id int not null, f int not null,
+primary key(f_id, id)) engine=innodb;
+create table t2 (id int not null,s_id int not null,s varchar(200),
+primary key(id)) engine=innodb;
+INSERT INTO t1 VALUES (8, 1, 3);
+INSERT INTO t1 VALUES (1, 2, 1);
+INSERT INTO t2 VALUES (1, 0, '');
+INSERT INTO t2 VALUES (8, 1, '');
+commit;
+DELETE ml.* FROM t1 AS ml LEFT JOIN t2 AS mm ON (mm.id=ml.id)
+WHERE mm.id IS NULL;
+select ml.* from t1 as ml left join t2 as mm on (mm.id=ml.id)
+where mm.id is null lock in share mode;
+id	f_id	f
+drop table t1,t2;

mysql-test/innodb_unsafe_binlog.test

+-- source include/have_innodb.inc
+#
+# Note that these test work only on 5.0 because these test need
+# innodb_locks_unsafe_for_binlog option implemented.
+#
+#
+# Test cases for a bug #15650
+#
+
+--disable_warnings
+drop table if exists t1,t2;
+--enable_warnings
+create table t1 (id int not null, f_id int not null, f int not null,
+primary key(f_id, id)) engine=innodb;
+create table t2 (id int not null,s_id int not null,s varchar(200),
+primary key(id)) engine=innodb;
+INSERT INTO t1 VALUES (8, 1, 3);
+INSERT INTO t1 VALUES (1, 2, 1);
+INSERT INTO t2 VALUES (1, 0, '');
+INSERT INTO t2 VALUES (8, 1, '');
+commit;
+DELETE ml.* FROM t1 AS ml LEFT JOIN t2 AS mm ON (mm.id=ml.id)
+WHERE mm.id IS NULL;
+select ml.* from t1 as ml left join t2 as mm on (mm.id=ml.id)
+where mm.id is null lock in share mode;
+drop table t1,t2;

row/row0sel.c

@@ -3972,12 +3972,12 @@ cursor lock count is done correctly. See bugs #12263 and #12456!
 	/* We have an optimization to save CPU time: if this is a consistent
 	read on a unique condition on the clustered index, then we do not
 	store the pcur position, because any fetch next or prev will anyway
-	return 'end of file'. An exception is the MySQL HANDLER command
-	where the user can move the cursor with PREV or NEXT even after
-	a unique search. */
+	return 'end of file'. Exceptions are locking reads and the MySQL 
+	HANDLER command where the user can move the cursor with PREV or NEXT 
+	even after a unique search. */
 
 	if (!unique_search_from_clust_index
-	    || prebuilt->select_lock_type == LOCK_X
+	    || prebuilt->select_lock_type != LOCK_NONE
 	    || prebuilt->used_in_HANDLER) {
 
 		/* Inside an update always store the cursor position */