- A substitution arg is categorized as "subst", but was tested for
"substitution".
- The Arguments::is_multipart method was triggering on '/', which is
wrong, but I can't remember why I put it in there. Hmmm.
- When extracting a write-filter, substitutions after the command
were generating an error, whereas they should be ignored.
- Task::substitute was modifying data even when the patterns were not
matching. Yikes.
- Added unit tests for en-passant modification of all types during
done, delete, start, stop.