Also fixes json-test output on finish, and allow to put both on err or
out (--out-only and --err-only).

…void misuse.

Use cache first in 'to_pod_full', for in between commits case.
Change dump activation to use a function pointer instead.

this case to reuse existing code.
Reuse of `storage_at` was not easy in this case (could not iterate and
use the method at the same time (refcell mutable borrow panics) so
keeping code as is.

Use 'base_storage_root' instead of 'storage_root'.
Added a test, it will only execute with json-test in ci, or when launch
with the feature.

Comments fixes.
Minor code changes.