HEAP tables can't index BIT fields. Due to this when grouping by such fields is
needed they are converted to a fields of the LONG type when temporary table
is being created. But a side effect of this is that a wrong type of BIT
fields is returned to a client.

Now the JOIN::prepare and the create_distinct_group functions are create
additional hidden copy of BIT fields to preserve original fields untouched.
New hidden fields are used for grouping instead.


mysql-test/t/type_bit.test:
  Added a test case for the bug#30245: A wrong type of a BIT field is reported when grouped by it.
mysql-test/r/type_bit.result:
  Added a test case for the bug#30245: A wrong type of a BIT field is reported when grouped by it.
sql/sql_select.cc:
  Bug#30245: A wrong type of a BIT field is reported when grouped by it.
  Now the JOIN::prepare and the create_distinct_group functions are create
  additional hidden copy of BIT fields to preserve original fields untouched.
  New hidden fields are used for grouping instead.