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.
Bump version to 3.1.0.47
Update the (debian) changelog
Add :compression support for dump-image on SBCL. Fix dump-image for SBCL/Windows.
Bump version to 3.1.0.48