user-homedir-pathname on cmucl

[Raymond Toy]

Not sure how this ever worked with cmucl, but user-homedir-pathname on
cmucl returns #p"home:", where "home:" is a search-list. In some
cases, it looks like asdf is trying to create the cache directory and
end up with a path like

P"home:.cache/common-lisp/cmu-21a__21a_unicode_-macosx-x86/**/*.*.~*~"

but this confuses other parts of asdf and cmucl when trying to run
pathname-match-p.

Perhaps the best thing is to make asdf us a custom
user-homedir-pathname like what is done with other lisps.  An
appropriate version would be 

(defun user-homedir-pathname ()
  (first (ext:search-list (cl:user-homedir-pathname))))

--
Ray