It so happens that we still need to compare actions by type of operation only.
Hide that under an abstraction.

Move deferred-warnings support to asdf-driver.

Make it work with CLISP 2.44 (modulo patch to cl-launch, now 3.20.1),
checking for LINUX symbols at runtime.
Graceful fallback to serial behavior on unsupported platforms.

* 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.

This is a major rewrite of several subsystems of POIU.
NB: it looks like some race condition it making things hard for us on either SBCL or CCL.
This isn't stable. Try POIU 1.027 with ASDF 2.26 for stable results.

external-format, *compile-op-compile-file-function*, compile-flags).
For that, depend on ASDF 2.21 or later (2.23 or later preferred).
Also, override any with-compilation-unit when compiling in a fork.
If that causes warnings you don't like to be emitted...
use asdf-condition-control.

* have system depend on asdf.
* know how to recover when signals dropped.
* define parallel-load-system, parallel-compile-system.
* make test executable as a shell script.
* I can make clisp break mostly reliably on fare-utils
 if both module pure and stateful depend on base as well as interface(!)
 it then claims "Cycle detected".