Don't send over useless verbose log messages.

When in :data logging mode we log the whole data set as we read then
write it, which is quite a lot of data. Our current logging system works
by filling up a queue that the cl-log lib is then fed from, and sending
lots of data in that queue is way expensive, stop doing that.

Hopefully we don't need to revisit the logs more than that, the other
messages should be few enough not to count much when doing a full load.