show that even \later^n False is inconsistent (for any fixed n); properly use pvs in counter_examples

Also cleanup the file a bit.

ticket lock

@jung merge?

See merge request !1

The new updates allow allocation fresh elements satisfying an arbitrary
proposition (for example, being even) instead of just not being in a given
finite set.

TODO: maybe also do this for finite maps (gmaps).

This makes clear that we do not range over Coq terms.

This change makes it possible to use hlists in the proof mode, which
itself uses hlists in the implementation of the specialize tactic.

This avoids recompilation of coq_tactics each time an instance is added.

The new implementation ensures that type class arguments are only infered
in the very end. This avoids the need for the inG hack in a0348d7c.

This way type class inference is not invokved when used in tactics
like iPvs while not having to write an @.

(Idea suggested by Ralf.)