Only add new constraints to the ConstraintState if they can be false.

This omits adding lots of tautologies to the state.
This means that only constraints containing symbolic values are added to the ConstraintState now, as
constraints only consisting of explicit values are either always true or always false (in which case the new state is unreachable).



git-svn-id: https://svn.sosy-lab.org/software/cpachecker/branches/symbolic@15011 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c