2.28.8: more consistently check whether or not to check warnings

Fixes lp#1122896
2.28.9: implement deferred-warnings support for CMUCL (and SCL?)

Low-level code provided by Raymond Toy.
2.28.10: fix issue with deferred warnings for setf foo functions in CCL 1.9.

Issue found by Bill StClair.
2.28.11: implement deferred warnings for allegro. Beef them up for CCL.

Many thanks to Duane Rettig for explanations on how to support Franz.
lisp-action cleaned up some more for deferred-warnings.
test-deferred-warnings beefed up.
CCL still isn't fully there yet, and needs to better detect
forward reference to macros.
Also, make safe-file-write-date NIL robust independently of implementation.
Test tweaks
Getting ready for a release 2.29.
2.29: blessing 2.28.11 as release
Update release infrastructure
Slight documentation update. Remove an obsolete file.
2.29.1: extend the (un)reify-simple-sexp protocol to handle simple-vector.

After testing by avodonosov, it was found this was needed to (un)reify
deferred-warnings on CCL.
2.29.2: CCL: punt on upgrade from ASDF2. load-asd: use global readtable.

Package upgrade on CCL still fails due to setf function issues.
Until they are resolved, punt if upgrading from earlier than 2.27.

iolib 0.7.3 modifies the global readtable, and is thus incompatible with
the with-standard-io-syntax in load-asd, unless we re-bind readtable
to preserve this dirty global thing. Until we fix iolib and all clients,
revert to higher compatibility.
Add TODO items. Add version tests.
2.29.3: fix issues found by stassats on CMUCL.
2.29.4: fix bad/obsolete exports found by stassats.
2.29.5: more fixing of exports, with test added.

Thanks to stassats for initial test code.
2.29.6: some filesystem tweaks to accommodate Genera (!)
Remove some debugging code from script-support.lisp
2.29.7: Fix some corner cases from testing with cl-test-grid.
2.29.8: avoid using reify-simple-sexp which only obscures errors

Also, some more tweak of exported symbol test, for ECL.
2.29.9: in load-asd, preserve *print-pprint-dispatch* as well as *readtable*.

Although I'd like to isolate .asd files from each other,
copy-readtable and copy-pprint-dispatch are slightly too expensive
to use lightly (cons 1648 and 2192 bytes respectively on CCL 1.9 x86-64,
and more like 5300 and 10300 bytes on SBCL 1.1.3 x86-64).
There is no portable way to ensure the tables are read-only, and
bad things can happen if they are mutated while bound to the standard defaults.
So for now, I'm doing the backward-compatible thing of letting users
take responsibility for binding and mutating them, or more likely for success,
avoiding to bind and mutate them.

Thanks once again to Anton Vodonosov for his help with cl-test-grid.