Fixes: lp#1042691 (thanks, stassats)

This fix is from Mr. Kiyoshi Mizumaru.  It adds an "S" to the
lisp-version-string in the ACL SMP case.

based on code by MKCL's Jean-Claude Beaudoin.

Tested: CCL, ECL, SBCL.

* Refactor load-system to use *load-system-operation*,
and change require-system and module-provide-asdf to use that.
* Remove broken-fasl-support: first, cormanlisp is supposed to have fixed it;
 second, cormanlisp is dead;
 third, one can now (setf *load-system-operation* 'load-source-op) instead.
* Reindent default-source-registry
* Fix a test in light of some previous package frobbing.

modulo remarks sent on the mailing-list.

This allows for consistency check of .fasl output before the file can possibly be seen
by other builds (i.e. no race condition).

Don't upgrade ccl or cmucl on older asdf's due to incompatibilities.
Shouldn't matter since they already ship with more recent versions of asdf.

Notably specify the inheritance behaviour of :encoding.

for which we do extra magic filtering. Should make Erik Pearson happy re lp#1000842.

Thanks to Erik Pearson for prompt bug report.

following discussion with Nikodemus on asdf-devel.
Also, improve the way we test for upgrade.
Disable upgrade test on cmucl from asdf 2.00*.
Restore -i.bak flag in bump-version: it's actually needed.

Update documentation somewhat.

to make Erik Pearson happy.

Fix a misparenthetization in 2.20.12 that disabled windows shortcut.

by using unintern rather than fmakunbound for redefined generic functions.