We now have decent wrapper scripts with even better ones on the way, so I think
there is no longer a need to have something like this directly by the
src/search/downward executable. (In fact, I think it's undesirable to duplicate
functionality in this way.)

Hence closing this.

Especially for small, informal experiments, it would be nice if the planner
could be run directly on PDDL inputs. To still allow the current mode of
operation, this could be optional, i.e., the planner could accept either PDDL
files or preprocessed output files. In the simplest implementation, the planner
would just call the translator and preprocessor via ::system.