Support of virtual columns added to maria engine.

mysql-test/suite/vcol/r/vcol_handler_maria.result:
  Basic tests for virtual column and maria engine.
mysql-test/suite/vcol/t/vcol_handler_maria.test:
  Basic tests for virtual column and maria engine.
storage/maria/ha_maria.cc:
  Support of virtual columns added to maria engine.
storage/maria/ha_maria.h:
  Support of virtual columns added to maria engine.