This bug manifested itself for queries with grouping by columns of
the BIT type. It led to wrong comparisons of bit-field values and
wrong result sets.
Bit-field values never cannot be compared as binary values. Yet
the class Field_bit had an implementation of the cmp method that
compared bit-fields values as binary values. 
Also the get_image and set_image methods of the base class Field 
cannot be used for objects of the Field_bit class. 
Now these methods are declared as virtual and specific implementations
of the methods are provided for the class Field_bit.


mysql-test/r/type_bit.result:
  Added a test case for bug #30219.
mysql-test/t/type_bit.test:
  Added a test case for bug #30219.
sql/field.h:
  Fix bug #30219.
  This bug manifested itself for queries with grouping by columns of
  the BIT type. It led to wrong comparisons of bit-field values and
  wrong result sets.
  Bit-field values never cannot be compared as binary values. Yet
  the class Field_bit had an implementation of the cmp method that
  compared bit-fields values as binary values.
  Also the get_image and set_image methods of the base class Field
  cannot be used for objects of the Field_bit class. 
  Now these methods are declared as virtual and specific implementations
  of these methods are provided for the class Field_bit.