Missing prepare-define-op

[Faré]

While fixing find-system for https://bugs.launchpad.net/asdf/+bug/1739514 I found that find-system should probably be refactored to somehow check timestamp for define-op, and that the definition-dependencies-up-to-date-p should not be a function, but a by-product of checking the timestamp when define-op depends on a prepare-define-op (to be defined) that will have a suitable component-depends-on to the operations in the definition-dependency-list.

I'm not going to fix it. This will be a great way for my successor to get acquainted with the deepest guts of the dependency traversal algorithm.

[Faré (fahree)]

The test case would be something like:
a defsystem-depends-on b.
b is modified.
b is loaded and now up-to-date (in the same image, without loading a).
Next time a is loaded, a.asd should be re-loaded because b was modified, but isn't.

To fix this bug, find-system would be refactored so it can directly use action-up-to-date-p on define-op. Define-op would have a new operation prepare-define-op as selfward-operation dependency. And prepare-define-op would depend on the definition-dependencies.