improved support of replication between tables of different structure

--binlog_row_metadata=full stores columns names and other metadata into the binary log.
However this is not used by replication threads, which can cause data loss on multi-master if one adds or drop fields with ALTER TABLE when binlog_format=row or binlog_format=statement is used.

ALTER TABLE will work if columns are added last to the table. However if one deletes columns or add a column in the middle of the table will cause all future DML to update wrong fields.

The fix is that if --binlog_row_metadata=full is used, we should not use field positions but instead use field names for insert and update when applying row events.
mariadb-binlog should also be update to show fieldnames instead of field positions if field names are available.

I will add a simple test case that one can use to verify the issue.

We should probably also add an option --slave_type_conversions=IGNORE_MISSING_COLUMNS to allow one to drop columns with ALTER TABLE