This is done for comparing old with new

Add the path cases without changing the whole logic

If we refer to a path `a.b`, we should mark `a.b` as used,
which is better than marking `a`.

Needed to make stdlib2-cc go through.

There were two errors. One in LayListIterable required a type annotation
and a tweak to markFree. The other in Vieew.scala required a cast, but this could be fixed
with better handling of pattern matching. path-patmat-should-be-pos.scala is a minimization.

x*? is x.type @reach @maybe. This was not recognized before.

Previously, we violated that assumption is we too the deep capture set
of a capture reference wiht singleton type.

Count in dcs exactly those locations where a cap gets replaced by a reach capability.

Also: In Recheck-apply, use deep capture sets of arguments in computing the
result alternative.

Drop restrictions on leaking reach capabilities in markFree.

Revise visibility criterion for paths.

Together these changes now implement a classical capability system with reach capabilities.
References that are used later after passing some arguments are already recorded in capture sets
of earlier stages (exception: closure results).

A deep capture set should not be shortened to a reach capability `x*`
if there are elements in the underlying set that live longer than `x`.