2.23.2: * add MKCL support based on patch by JCB (see mailing-list).

* Refactor load-system to use *load-system-operation*,
and change require-system and module-provide-asdf to use that.
* Remove broken-fasl-support: first, cormanlisp is supposed to have fixed it;
 second, cormanlisp is dead;
 third, one can now (setf *load-system-operation* 'load-source-op) instead.
* Reindent default-source-registry
* Fix a test in light of some previous package frobbing.