Post-merge fixes#2: - A certain problem with NULLs filtering was solved in two different    ways. Use MWL#128's approach (it's more generic) and rollback DS-MRR's.
Post-merge fixes#2:
- A certain problem with NULLs filtering was solved in two different 
  ways. Use MWL#128's approach (it's more generic) and rollback DS-MRR's.

flynn1973/mariadb-aix,slanterns/server,flynn1973/mariadb-aix,natsys/mariadb_10.2,flynn1973/mariadb-aix,davidl-zend/zenddbi,natsys/mariadb_10.2,flynn1973/mariadb-aix,davidl-zend/zenddbi,flynn1973/mariadb-aix,flynn1973/mariadb-aix,davidl-zend/zenddbi,ollie314/server,natsys/mariadb_10.2,davidl-zend/zenddbi,flynn1973/mariadb-aix,natsys/mariadb_10.2,flynn1973/mariadb-aix,natsys/mariadb_10.2,davidl-zend/zenddbi,flynn1973/mariadb-aix,davidl-zend/zenddbi,ollie314/server,davidl-zend/zenddbi,ollie314/server,ollie314/server,ollie314/server,natsys/mariadb_10.2,ollie314/server,natsys/mariadb_10.2,natsys/mariadb_10.2,davidl-zend/zenddbi,davidl-zend/zenddbi,natsys/mariadb_10.2,flynn1973/mariadb-aix,davidl-zend/zenddbi,natsys/mariadb_10.2,davidl-zend/zenddbi,ollie314/server,ollie314/server,ollie314/server,ollie314/server,flynn1973/mariadb-aix,natsys/mariadb_10.2,ollie314/server