Just a proposition for a more controllable why3replayer

can be used with the task in a session

Too bad, it does not seem to support quantifiers...

This reverts part of commit b45604c2.

- Broken copy of image files.
- Broken copy of proof files if run from outside the session directory.
- Broken creation of directories inside the session directory.
- Silent incompatibility between some options.

it is safer to construct the whole pattern from an untyped skeleton
in a top-down way, than to check the ghostness/mutability on each
constructor application.