Gerber is a weird format, and I'm fixing things as I discover problems - today it was the fact that eagle sometimes exports rounded rectangles as lines drawn with a thick circular aperture.

Without any special handling, that meant the resulting holes in the stencil were too small because the line thickness was being ignored. Now, shapes drawn with thick apertures should be supported properly - though the edges still aren't rounded. This seems like a decent compromise, as 3D printers add rounded edges anyway and it's a lot easier to implement, but it might be that at some point someone wants to draw very large obround shapes by using a line with a big aperture, which won't work.

I also had to fix a bug in the underlying gerber library while I was at it - it didn't assign units for apertures, resulting in using inch values interpreted as cm.