gEDA-user: pcb insulator layer

[DJ Delorie]

> That's pretty cool. I looked at output logs for a set of gerbers
> produced with a commercial PCB tool, and it seemed that they had output
> gerbers which combined from multiple internal layers.

I've been thinking that pcb needs a "cam" exporter, which can do
various permutations of the existing data as per a cam script, and
feed it to one of the other exporters.