Fixed two bugs in Grounder.

* Fixed: Solver::Assign() would check for inconsistency too early.
* Fixed: Solver::ResolveDeterminateTerms() would only check
  non-primitive intead of only checking for primitive terms.
* Fixed: Solver::ReduceComplete() needs to check if clause is valid
  before checking for subsumption as Setup only wants to see
  non-valid clauses.
* Added KR-2016 and ECAI-2016 examples to unit tests.