added "spass_tptp" prover, which requires SPASS x.y > 3.0;
once users have upgraded their SPASS and we have determined that "spass_tptp" works well, we can make "spass_tptp" the one and only "spass"
Bool = FOL +
types bool 0
arities bool :: term
consts tt,ff :: "bool"
end