In my case, they are really holes, not slot. Namely, alternative part pattern of a transformer: 5 pins (100 mils) with missing center pin or 4 pins (150 mils). The middle 2 pins get very close, if not touching. I can probably use slot, if i can figure out how to do that with the linux gEDA pcb. It only allow me to insert holes, not slot.
If i do it in gerber, how do i specify slot?
This is for hole: M48 INCH T41C0.020 % T41 X006000Y034500