Returning plugin::UNKNOWN_ERROR in a TransactionApplier makes data disappear

[Marcus Eriksson]

If i return plugin::UNKNOWN_ERROR in the apply(...) method of a plugin::TransactionApplier subclass, the data that is being inserted is lost without any feedback to the client (i.e. it looks to the client as if the transaction was OK, but it was actually rolled back)

Expected behavior should be to report an error back to the client