Prevent replication if slave has no log and store is not empty

When a slave has no transaction log, the replication  bootstrap from the begnining. If there are already some data in the slave store, there is something wrong that need to be investigated rather than bootstrapping again.
Remove dead code
Merge pull request #224 from wajam/manu-slave-nolog-consistency

Prevent replication if slave has no log and store is not empty