Photocopiers now copy stamped papers

A new attempt on having photocopiers copy stamp overlays.
Instead of using icon vars now, there are now simply three new states in bureaucracy.dmi, resembling the three different shapes a stamp can have, desaturated.
![error](http://i62.tinypic.com/1zny3hf.jpg)
Original on top, copies on the bottom.
Now works well with carbon papers as well, and one is now actually able to photocopy copies. Derp.

There's also a minor bugfix covering the issue that stamping a paper would not draw a horizontal line to separate text from stamp information.