gEDA-dev: code sprint ideas

[DJ Delorie]

> You want rounded clearances, but square soldermask apertures.
> 
> In the example above, all but the pad would be covered with soldermask.

Except that fabs won't let you do that; they want the mask to be
bigger than the pad by some amount, in case of registration errors.
If you're using a 3 mil gap and 6/6 rules, an offset mask could
uncover some adjacent copper near the corner.  With a 3 mil gap
(i.e. +- 3 mil mask accuracy), you could end up with 6 mil on two
adjacent sides, or 8.4 mils from the pad's corner to the mask's
corner.  If you have a 6 mil copper clearance, you've just uncovered
2.4 mils of the wrong copper.