Fix regression whereby ASDF 3.0.3 warns but still loads an old ASDF.
Also decline to "upgrade" to very same version, but without warning. Add a regression test. You can see the test fail with old versions, with e.g. cat build/asdf-3.0.3.lisp > build/asdf.lisp ; make t l=ccl t=test-sysdef-asdf.script Also tweak ensure-gethash to return two values, and add tests.
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