Fixed: Reground() missed inconsistency after G.

When new clauses made the setup inconistent
(add_result == Setup::kInconsistent), this result could be lost after
the re-adding of relevant clauses in case p.relevant.filter == true.

This is fixed now: Reground() terminates if add_result is
Setup::kInconsistent after adding newly grounded clauses.

The wrong add_result was a problem because it is passed to
Grounder::AddClause() and returned there, and then used by
Solver::Split() and Solver::Fix() to decide further actions.