1.29: since 1.027 a major refactoring of POIU that works well with ASDF 2.26.15.

1.29: since 1.027 a major refactoring of POIU that works well with ASDF 2.26.15.
* Using files, not pipes, to communicate results, to avoid deadlock due to full buffers.
* Major simplification by hooking into recent ASDF's perform-plan interface,
 rather than kludging our way around perform for parallel operations.
* Take advantage of ASDF 2.26.15's new internal traverse and action-stamp APIs.