Also add solve with three assumptions to SimpSolver.
Also add solve with three assumptions to SimpSolver.

meteor/minisat,jamesbornholt/minisat,niklasso/minisat,mabdula/minisat,robertsami/minisat,meteor/minisat,niklasso/minisat,robertsami/minisat,mabdula/minisat,meteor/minisat,mabdula/minisat,jamesbornholt/minisat,meteor/minisat