Consider raising the default validation_output limit

[Matistjati]

8 MiB feels like cutting it a little close with output visualizers. I would be much more comfortable with e.g. 16 or 32. I think it's unlikely that we would ever need to increase it beyond 32, and don't really see any major drawbacks. Maybe some pipe could fill up...?

[niemela]

I think this would make a lot of sense. Note though, that it is not a "default" limit, it's a "typical system default".