[gta02-core] Silk screen over copper

[Werner Almesberger]

While fiddling with fped, I noticed that we have quite a few
footprints with silk screen drawings over copper pads:

DFBM-CS320 EXC24C FA2012 FH23-39S-0.3SHW LIS302DL miniUSB_B SC70-5
SC89-6 SON1408-3 SOT23-5 VSSOP8 TDFN34-16 TSOP-6 WM8753FL

KiCad will take this "as is" and not make holes in the silk screen
for the pads. It's anyone's guess what a PCB maker will make with
it.

These conflicting drawings in general show the package outline,
which is also useful information, but this is something that would
better go into a 3D package drawing. It may actually be possible
to automatically generate some 2.5D package drawings from the
information in fped without too much effort. I need to think about
this some more.

Fun KiCad problems found along the way:

- I'm getting thin (1 mil) silk lines around pads. I never noticed
  this before. Not sure yet if it's a quirk of our setup or a
  general bug in KiCad.

- when viewing our board in 3D, the arcs come out all wrong. But
  the result actually looks quite beautiful :-)

By the way, the next time you update fped, please rebuild it with
make clean all
I changed the way the icons are converted and this is not a change
the make dependencies can detect. With the old XPMs, fped should
still work but will look slightly uglier.

- Werner