The repository should check if the WAL contains any unfinished tasks

[evert]

Upon receiving a CRUD operation, the repository should check if the WAL contains any unfinished secondary tasks for that record.
These operations should then be executed first before the new operation can be accepted and performed.

[evert]

r4236

CRUD operations check if the WAL contains any unfinished secondary tasks, and executes them first.
Messages have a try count for each consumer. Each time a message is tried to be processed, the try count is increased. When the try count reaches the maxTries defined by the consumer, the message is marked as problematic. Problematic messages are no longer picked up by RowLogConsumers?, but can still be processed by calling RowLog#processMessage?().