2.26.102: fix issues on ECL, maybe CLISP too, improve version bumper.

Move things around and rename functions to improve backward compatibility.
The driver now has its own backward-compatibility file.
More ECL bundle fixes.
2.26.103: bump version after previous fixes.
Also, fix the generate-asdf.asd system.
2.26.104: get program-op to work alright on ECL.

Some attempts at making things work for ABCL and CLISP.
2.26.104: some more pathname munging.
2.26.106: a new primary/secondary convention for subsystems and more

A system named foo/bar will be looked up in a registered file foo.asd.
This makes it possible to sensibly name several systems in a .asd file
and still have asdf find them all by name.
We now use it to not have the asdf header be part of asdf-driver.

A new generic operation build-op makes it possible to deal with
the fact that the default operation for systems need not be load-op,
yet that the end-user does not want to have to know the exact operation
for each of the system he uses.

ensure-pathname has been improved again, and its clients tweaked.

remove-keys was made more sensible by using EQL rather than STRING-EQUAL.

:version need not take the first form in a file, but can take
a path to a subform. This makes it possible to get the exact subform
in a Lisp source file that has the string.
See SUB-OBJECT for how these paths work.

Cleanup of the semantics of ENSURE-FUNCTION on CONSes: use APPLY, not EVAL.
Update some tests
2.26.107: make logical pathnames work. Gah.
2.26.108: tweak locate-system after previous change. Fix some tests.
2.26.108: fix the "new export" case of define-package.
2.26.110: Fix omission in previously insertd assertion.
Tests now pass on SBCL.
2.26.111: fix embarrassing bugs in ensure-pathname
2.26.122: Replace if-bind by if-let from alexandira.

Have one bigger lisp script to replace several shell scripts.
2.26.113: export file-component.
Rename the asdf-only archive into asdf-system.
2.26.114: import the deferred warnings support from POIU to ASDF-DRIVER.

Still not used by ASDF itself.

Also, don't use compile-file-pathname after all, it's a bad idea,
since we may be loading a .asd from within an eval-when during a compile-file,
but we won't be compiling the .asd.
2.26.115: more fixes to version access. Now works with POIU 1.29.6.
2.26.116: Avoid stepping on symbols used by ASDF 2.26 and earlier
unless we're backward compatible.
2.26.117: fix setf symbol frobbing on CLISP.

Also remove some forgotten debugging statement,
clean the asd somewhat.
2.26.118: rename asdf/generate to asdf/defsystem,
also use asdf-defsystem as the name for packaging.