The rpl_trigger test case indicated a problem with idempotency support when run
under row-based replication, which this patch fixes.

However, despite this, the test is not designed for execution under row-based
replication and hence rpl_trigger.test is not executed under row-based
replication.

The problem is that the test expects triggers to be executed when the slave
updates rows on the slave, and this is (deliberately) not done with row-based
replication.