INSERT DELAYED inserts garbage for BIT columns.

When delayed thread clones TABLE object, it didn't adjusted bit_ptr
to newly created record (though it correctly adjusts ptr and null_ptr).

This is fixed by correctly adjusting bit_ptr when performing a clone.
With this fix BIT values are stored correctly by INSERT DELAYED.


mysql-test/r/delayed.result:
  A test case for BUG#26238.
mysql-test/t/delayed.test:
  A test case for BUG#26238.
sql/field.h:
  Added move_field() to Field_bit class. When moving a field, adjust
  bit_ptr also, which is specific to Field_bit class.