index column

There was actually two problems
1) when clustered pk, order by non pk index should also
compare with pk as last resort to differ keys from each
other
2) bug in the index search handling in ha_partition (was
found when extending the test case

Solution to 1 was to include the pk in key compare if
clustered pk and search on other index.

Solution for 2 was to remove the optimization from
ordered scan to unordered scan if clustered pk.