gEDA-dev: [pcb] thin lines for assembly layer?

[DJ Delorie]

For one of my recent footprints, I added an 0.01 mil silk where the
physical part was, so I could verify the pads and such.  It got me to
thinking, maybe we could special-case "thin" silk to be used for the
assembly drawing?  I.e. if silk is <0.1mil, it's not drawn on the
regular silk print, but is drawn on the assembly print.  For the GUI,
it's drawn just like it is now.

I'd rather have a special layer just for assembly, but that means
adding to the Element file format and major changes to pcb to support
it all.  The thin-silk change is a hack, but a small hack and no file
format changes are required.

Thoughts?  Should we wait until the hard "more layer types" change is
made, or add the hack now?