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.

mysql-test/r/partition_innodb.result:
  Bug#37721: ORDER BY when WHERE contains non-partitioned
  index column
  
  updated test result.
mysql-test/t/partition_innodb.test:
  Bug#37721: ORDER BY when WHERE contains non-partitioned
  index column
  
  Added test case for bug verification.
sql/ha_partition.cc:
  Bug#37721: ORDER BY when WHERE contains non-partitioned
  index column
  
  using m_curr_key_info with both given index and PK
  if clustered PK.
  Also including PK in read_set.
  Added debug prints for easier verification.
sql/ha_partition.h:
  Bug#37721: ORDER BY when WHERE contains non-partitioned
  index column
  
  Changed m_curr_key_info to a null terminated array
  with max 2 keys and a terminating null.
  For use with key_rec_cmp with both given index and PK.
sql/key.cc:
  Bug#37721: ORDER BY when WHERE contains non-partitioned
  index column
  
  added handling of a null terminated array of keys for
  use in compare.