From version 6.19 onwards clc does not longer add the 
/usr/share/common-lisp/systems/ directory to asdf:*central-registry*

The net effect of this is that just using "(asdf:oos 'asdf:load-op ...)" 
will no longer work. The only way to load clc enabled packages now
it to use "(clc:clc-require :<foo>)"

You can also activate the clc packages using "clc:with-clc-active" so

(clc:with-clc-active
  (asdf:oos 'asdf:load-op :<foo>))

will work too.

This change was done so that using for example clbuild in Debian becomes
possible again. Otherwise the packaged systems will interfere with the
clbuild or locally generated systems.