Upgrade failures for asdf-3.1.7 and later

Starting with a bare lisp image (e.g --no-userinit --no-sysinit for SBCL), the following signals a "component not found" error:

(load "asdf-2.26.lisp") ;;; or whatever system you want (push #p"~/quicklisp/dists/quicklisp/software/alexandria-20170227-git/" asdf:*central-registry*) (load "asdf-3.2.1.lisp") (asdf:load-system "alexandria")

The first bad commit is https://github.com/fare/asdf/commit/3a9457a

I hope this wasn't intentional? Ideally an old asdf version would never get loaded, but practically speaking it sometimes does (e.g. on LispWorks PE and CLISP). And if that happens, thereafter one is unable to load a system that requires asdf-3. The above case is a whittled-down version of a quickloading problem.

Best, lmj