EXTRA COLUMN ON SLAVE

Analysis: In prepare_record(), which is called to prepare the
basic record, we call restore_record to fill the tuple with
all the default values which are maintained in memory at
table->s->default_values. But for the special DEFAULT clauses
like DEFAULT CURRENT_TIMESTAMP/NOW(), it is not maintained
in table->s->default_values. It will be populated only when
we explicit ask to do it (i.e., calling set_default()) function.

Fix: For the extra fields that are present only on slave and  that
does not have 'DEFAULT' clause, replication calls 'set_default()'
which will fill the record with default values (like for integer
types 'zero' even though there is no DEFAULT 0 for the field).
This logic is executed only for the field's that does not have
default clause. Now the logic is extended to call set_default when
there is special default clause (has_insert_default_function()).