- all conflict errors are counted and logged at info, as they were before Florent's change
- logging makes it clear where the conflict has been resolved and where it hasn't
- errors seen by the user are rendered with standard_error_message and are sent to the error_log which will likely copy them to the event log, depending on the users setup.
- also checking in a functional test for generating write conflict errors.

(I'll be committing to CHANGES.TXT shortly, I just wanted to keep the merges simpler)