MDEV-5177: ha_partition and innodb index intersection produce fewer rows (MySQL Bug#70703)

(This is attempt at fix #2) (re-commit with fixed typo)
- Moved the testcase from partition_test to partition_innodb.test where it can really work.
- Made ordered index scans over ha_partition tables to satisfy ROR property for 
  the case where underlying table uses extended keys.

mysql-test/t/partition_innodb.test

@@ -716,5 +716,52 @@ GROUP BY 1, 2, 3;
 
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-5177: ha_partition and innodb index intersection produce fewer rows (MySQL Bug#70703)
+--echo #
+create table t1 (
+  a int not null,
+  b int not null,
+  pk int not null,
+  primary key (pk),
+  key(a),
+  key(b)
+) engine=innodb partition by hash(pk) partitions 10;
+
+insert into t1 values (1,2,4); # both
+insert into t1 values (1,0,17);  # left
+insert into t1 values (1,2,25);   # both
+
+insert into t1 values (10,20,122); 
+insert into t1 values (10,20,123);
+
+# Now, fill in some data so that the optimizer choses index_merge
+create table t2 (a int);
+insert into t2 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+
+insert into t1 select 1,2, 200 + A.a + 10*B.a + 100*C.a from t2 A, t2 B, t2 C;
+
+insert into t1 select 10+A.a + 10*B.a + 100*C.a + 1000*D.a,
+                       10+A.a + 10*B.a + 100*C.a  + 1000*D.a, 
+                       2000 + A.a + 10*B.a + 100*C.a + 1000*D.a
+                       from t2 A, t2 B, t2 C ,t2 D;
+
+# This should show index_merge, using intersect
+--replace_column 9 #
+explain select * from t1 where a=1 and b=2 and  pk between 1 and 999999 ;
+# 794 rows in output
+create temporary table t3 as
+select * from t1 where a=1 and b=2 and  pk between 1 and 999 ;
+select count(*) from t3;
+drop table t3;
+
+# 802 rows in output
+create temporary table t3 as
+select * from t1 ignore index(a,b)  where a=1 and b=2 and  pk between 1 and 999 ;
+select count(*) from t3;
+drop table t3;
+
+drop table t1,t2;
+
 
 set global default_storage_engine=default;