Clarified error messages related to unsafe statements:
- avoid the internal technical term "row injection"
- use 'binary log' instead of 'binlog'
- avoid the word 'unsafeness'
Problem: the test syncs slave by a 'wait_condition' waiting until
table t1 has 5000 rows. However, there is no guarantee that t1
makes it to the slave before the wait_condition.
Fix: sync_slave_with_master just after t1 was created.
