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.

Cleanup the search-for-system-definition protocol.
Define upgrade-asdf function.
Cache the source-registry scan in a hash-table.

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

Also, allow for upgradability from old ASDF versions that don't have system-source-file.

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.

* work with Common Lisp Controller by disabling it for testing

* tweak test-retry-loading-component test

* tweak test-module-pathnames for CLISP (which can return
  `nil` for component's relative-pathname)

* refactor `component-relative-pathname` for source-file's
  slightly

* apply patch to better handle relative source-file types (from Fare Rideau)

* improve logic of tag updating in bump-revision-and-tag.sh

* make test output nicer (from Fare Rideau)

* improve test-module-pathnames (from Fare Rideau)

* apply patch to better handle relative source-file types (from Fare Rideau)

* improve logic of tag updating in bump-revision-and-tag.sh

* make test output nicer (from Fare Rideau)

* improve test-module-pathnames (from Fare Rideau)

    * test for same

* Fix for my head-slap regex s&r madness.