"Merge table does not work with bit types"
   MERGE should have HA_CAN_BIT_FIELD feature bit set or else table row is
   formatted incorrectly.


mysql-test/r/merge.result:
  Bug#19648
    Test for fix
mysql-test/t/merge.test:
  Bug#19648
    Test for fix
sql/ha_myisammrg.h:
  Bug#19648
    Must have HA_CAN_BIT_FIELD for BIT type support