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.

Remove debugging code from previous commit.

The issue fixed is that most Lisps don't like
*default-pathname-defaults* being a logical-pathname.
Added a test for logical-pathname functionality;
it all works on CCL, and works better on other Lisps after the fix,
but there are still logical-pathname issues on SBCL, CLISP and more.
Also, a package cleanup of our test suite.

Use probe-file for probe-file* in LispWorks.

Make ABCL's jar translation happier with
the recent compile-file-pathname* change for Stelian by redoing cfp myself.

Make truenamize work when the merged pathname is relative.
Makes it happier when e.g. the *default-pathname-defaults* is #p"",
which is the case notably on CCL.

Try and fail to support GCL 2.6 and have 2.7 fail less;
too many bugs, in CONDITIONs, PATHNAMEs, and more,
plus compiler bug that breaks coerce-pathname.

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

Simplify test scripts.

perl -pi.bak -e 's|"../asdf"|\(compile-file-pathname "../asdf"\)|;' *.script

* made it easier to debug tests. export DEBUG_ASDF_TEST=t
* add ECL support to tests: passes all 18 scripts, but have to ignore compile warnings.
* lots of whitespace issues, including ones that made .gitignore not work!

Found that the current load recipe (load "../asdf") in the test
scripts was brittle, because the presence of asdf.fasl was obscured
if there was an "asdf/" directory in ..  Unfortunately, the result
of makeinfo --html asdf.texinfo created just such a directory!
fe[nl]ix kindly provided a pointer to compile-file-pathname that
solved the problem.

the keyword package into ASDF (where it belongs!). Also added a new
test to exercise the restart and make sure it is what it claims to be.