where it ought to always have been, based on a properly cleaned up prepare-op
(previously introduced in 2.26.14 as parent-load-op).

This is a checkpoint of a mostly working system after major changes;
it requires further cleanup and fixes:
strangely, fails some tests on CCL but not SBCL.

Introduce find-operation as a companion to find-component,
subsuming make-sub-operation.
The results of component-depends-on are processed with find-operation and resolve-component-spec.
component-self-dependencies is fixed to play well with prepare-op.

Also, some internal renamings and signature changes:
parent-operation becomes upward-operation
parent-load-op becomes prepare-op
parent-source-load op becomes prepare-source-op
parent-component is distinguished from module
module-components becomes component-children
module-components-by-name becomes component-children-by-name
compute-module-components-by-name becomes compute-children-by-name
circular-dependency-components becomes circular-dependency-actions
component-load-dependencies becomes component-sibling-dependencies (with a stub)
introducing child-component, downward-operation.
refactoring visit-dependencies to include the loop in which it's always used.
refactoring force and force-not processing to use a function action-override-p;
force is achieved with a trivial method on operation-done-p for prepare-op,
and force-not as a trivial check in visit-action.

Tweak tests along the way. Tweak the documentation.

Failed to either rename operation-error or introduce action-error in its superclasses:
that breaks sb-grovel.

Fix wild-modules to work nicely well with ASDF2.
Allow to pass multiple script arguments to run-tests.sh.
Tests now pass on ABCL.

Show a good example: use (require :asdf) instead or (require 'asdf).

Some glue that won't affect too many people but that lets ASDF cleanly
hook the extensible PROVIDE/REQUIRE mechanism in upcoming SBCL 0.7.13

Fix wild-modules to not object when we call (setf (module-components))
on a new or about-to-be-reinitialised module.  We need to be able to
do this to get the weeds out, so it should be legal

wild-pathname-based modules for asdf.
(:wild-module "name" :pathname "foo/*.bar" :component-class 'bar-file), e.g.