Tests: SBCL passes test-lisp and test-upgrade
Also:
* big refactoring of test infrastructure
* contrib/debug.lisp and (asdf/driver:asdf-debug) for debugging.
* remove aif and it, use the cleaner if-bind.
* backtrace support, with improvements from trivial-backtrace.
* integration of asdf-condition-control (originally from xcvb-driver)
* simplify the upgrade heuristic: always tries to upgrade once.
  The previous heuristic was too complex with too many failure cases.
  You are thus assumed to want a given version asdf
  if and only if it is in your source-registry.

This restores the feature of do-first that was lost while refactoring ASDF
to fix the timestamp propagation issue.

The old asdf-bundle worked implicitly because of do-first:
fasl-op DEPENDS-ON compile-op, and compile-op has a DO-FIRST on the
load-op of dependencies, NOT a DEPENDS-ON, so if the compile-op is
"done" (which did NOT check the timestamps of dependencies),
then the dofirst is never consulted and load-op is never traversed.
In our new ASDF, we want to always traverse the load-op of dependencies,
so we can propagate their timestamps; however, we still want to only
actually load them if they are needed. Therefore, visiting actions
takes an additional flag "needed in this image", and each visited action
can be planned or not planned yet, and a not planned yet action can
be visited a second time to plan it after recursively visiting its
dependencies with the "needed" flag set.

Tests were fixed now to work now that this distinction exists.

Also, use coerce-pathname in asdf-ecl and deprecate merge-component-name-type.