Added a check for inconsistency for better performance.

Avoid recomputation of PEL particulalrly for inconsistent belief levels.
Fixed: forall x phi as not exists x _not_ phi.

The second negation was missing.
Fixed: context_copy_with_new_actions() mishandled query_zs.

* Fixed: query_zs only by accident had the correct value before;
  it shouldn't be changed when adding actions.
* Renamed context_copy_with_new_actions() to context_add_actions()
  which modifies the context in-place.
* Renamed query_entailed_by_setup() to query_entailed().
* Removed query_entailed_by_bat() (still exists in unit test only).