Keep name of target dataset (avoid reutilizing fktables)

Created by: scarlehoff

Reutilizing fktables is not well tested enough to work in all cases (and @RoyStegeman has already found bugs when he eliminated cfactors and different fktables started "being the same") so for now let's remove that possibility.

We can revisit it with the new commondata (when the reutilization of fktables by different datasets will also be more obvious)