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.

TODO: Create a define-package that can make it upgrade itself.

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.

* 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

* Improve error message for bad dependencies
* New default is for test-op to depend on load-op
* tweak run-program for SBCL so that ACL isn't #+no #+no bothered
* tweak write-test-web-page and write-license
* tweak some tests

ACL's compile-file-pathname is slightly broken; worked around it.
Made run-tests.sh executable.

	added make-defined-systems-table (unexported)
	(re)applied Luis Oliveria's patch to add a restart for missing
	components. This patch works in SBCL but not in Allegro Common
	Lisp or CLISP. The problem has to do with the computation of
	restarts and I'm still trying to figure it out. Since the
	failure doesn't cause any _new_ problems (it just means that
	the putative new restart isn't listed), I'm still committing.

	* asdf.lisp

	tests for the above

	(new) test/test-retry-loading-component-1.script
	(new) test/try-reloading-1.asd
	(new) test/try-reloading-dependency.hidden