Ignore preprocessed files *.pab

Delete all old *_p.ab preprocessed files

Modify preprocessed file name from *_p.ab to *.pab

- remove abduction after goal not_expect in consider_st2_aux
- add timestamp information after pending updates (cf. updates/1)
Add trolley problem exampes and fix features dealing with counterfactuals, particularly in preprocess.P (processI/1 and processPred/1).
Forget to add trolley problem examples in previous commit
Major fix of compute/7, define ensure_ground/1, and add "pregnant" example (from Byrne's book).

Define ensure_ground/1, where gensym is used for skolemization.
(just simple grounding, particularly for "pregnant" example to work)

Fix compute/7:
- Test first whether the called literal (either fluent or abducible) true, before calling bagof.
The previous version immediately calls bagof and using 'if/else' calls most_recent. It has a problem of looking for another abductive solution, as the 'if/else' construct actually introduces 'cut'.
- use copy_term/2 to make a copy of arguments (and input context) so they are not instantiated, when testing the called literal true and afterwards when bagof for that literal is called.