BUG#35850 "Performance regression in 5.1.23/5.1.24"

- Disable the "prefer full scan on clustered primary key over full scan
  of any secondary key" rule introduced by BUG#35850.
- Update test results accordingly 
(bk trigger: file this for BUG#35850)

mysql-test/t/innodb_mysql.test

@@ -13,3 +13,19 @@ let $test_foreign_keys= 1;
 set global innodb_support_xa=default;
 set session innodb_support_xa=default;
 --source include/mix1.inc
+
+--disable_warnings
+drop table if exists t1, t2, t3;
+--enable_warnings
+#
+# BUG#35850: Performance regression in 5.1.23/5.1.24
+#
+create table t1(a int);
+insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+create table t2 (a int, b int, pk int, key(a,b), primary key(pk)) engine=innodb;
+insert into t2 select @a:=A.a+10*(B.a + 10*C.a),@a, @a from t1 A, t1 B, t1 C;
+--echo this must use key 'a', not PRIMARY:
+--replace_column 9 #
+explain select a from t2 where a=b;
+drop table t1, t2;
+