lisp-invocation: play nicer with recent SBCL.
disable rucksack for now until issues with latest SBCL are resolved.

driver: Be more robust when borking or otherwise dying.
TODO: ABCL fork hints.

* More but still incomplete support for mkcl and cormanlisp.

Also export some command-line related symbols from the driver.

into the encodings feature. utf-8 is the default encoding and use :default
at your own risk. Anything else gets delegated to asdf-encodings.

Make sure we (re)initialize-asdf at some early point: things may have changed after image-dump.

Fix tests with SBCL, too.
Remove obsolete setup.lisp for good. We are in an asdf 2 world!

Fix build with xcvb wrt fare-memoization change.

Handle exit codes when running from the Lisp REPL.
Driver tweaks; notably control conditions when loading an ASDF system.

Notably, pass around the location of the xcvb-program we create in the cache.

This allows the examples to be created without having to install
an XCVB. The primary implementation is in bootstrap.lisp and
additional code in driver.lisp.
+ The created XCVB is made with one of the supported lisp
implementations even though the enclosing lisp invocation might
not be.
+ Refactored lisp-invocation into its own package.
+ The cache-description file contains notes about how the cache
should function. The cache is both the multi-user cache as in
distcc, ccache, etc, but also the user specific workspace for
where to dump fasl files and whatnot.