[asdf-devel] Test for ASDF system in jar archive with ABCL

The ABCL contribs are all defined via ASDF in a jar file, so the test is simply to try to load one of them, here JSS. Not all downstream packaging systems include the abcl-contrib.jar, so I try to guard against a false negative with an UNLESS clause in the abcl-contrib REQUIRE, but in my testing by removing abcl-contrib.jar this didn’t seem to work correctly. -- "A screaming comes across the sky. It has happened before but there is nothing to compare to it now."