Source ASDF systems residing in jar files may now be repackaged, as
was the usually case for JSS which prompted this rework.

We now neither package nor read fasls from jar files by default for
two reasons.  First, configuring ASDF to not compile systems seems to
have changed somewhat, so the finagling of output translations no
longer seems to work.  Secondly, since the Lisp compiler is always
present at runtime, fasls can always be created provided that ASDF has
writable local directory, which would probably be true in almost
all (?) deployment scenarios.

We now attempt to package non-source artifacts declared in system
definitions via asdf components that are files but not compiled
artifacts as well as those which appear in the
ASDF/COMPONENT::ADDITIONAL-INPUT-FILES slot.

We have removed use of ASDF internal symbols as much as possible, but
alas still use a couple internal interfaces where unavoidable.

We no longer use the deprecated ASDF:*CENTRAL-REGISTRY* to add systems
to the source registry.

Resolves <https://github.com/armedbear/abcl/issues/476>.