so it's less of a special case from how task definitions generally work.
* Key packages are always included in a task, and need not be explicitly
listed by the Packages field, although it's ok if they are.
* Allow package list programs to output the list separated by any
whitespace, not just newlines.
* Pass params from Packages: fields to the program that is run.
* Add a "list" method, supporting easy user-defined tasks with no coding
or overrides hacking needed, vis:
* Some docs improvements in this area.