gEDA: pcb thindraw epiphany

[DJ Delorie <dj@xxxxxxxxxxx>]

I was thinking recently about layering HIDs.  I'm using two HIDs for
EPS export; one just gathers data and the second does the actual
drawing.  I'll probably use the same trick for gerber, since we need
to enumerate the apertures.  Anyhoo, I was also fixing a bug in the
lesstif layer that I noticed while using thindraw, and a thought
occurred to me.  Previously, I had decided that "thindraw" was a
HID-specific thing; the core didn't need to have the logic to
implement thindraw (hence the separate "trace" and "pad" end caps :).
The new thought was that we could have a "thindraw HID" that did
nothing but convert the desired drawing commands (line, circle, etc)
to thindraw commands, and pass them along to the underlying HID.

Not only does this mean all the GUIs get thindraw with little effort,
but we can also do thindraw Postscript or EPS plots.  Since the EPS
plots stack all the layers, and can't support the masking we need for
polygon clearances, I think thindraw would be useful there.

Comments?