Issue: ADJUST-ARRAY-NOT-ADJUSTABLE (Versions 2a,2b,2c)

[David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>]

I strongly oppose ADJUST-ARRAY-NOT-ADJUSTABLE:SIGNAL-ERROR and
ADJUST-ARRAY-NOT-ADJUSTABLE:SIGNAL-ERROR+NEW-FUNCTION, since they would
break an existing implementation (Genera) by forcing it to enforce the
:ADJUSTABLE keyword for all arrays.  Currently Genera includes the
extension that all non-displaced arrays are adjustable (on Ivory, displaced
arrays are also adjustable).  There may be other implementations with
similar extensions.  Such a change would probably break large numbers
of user programs that were never intended to be portable and don't
bother with the :ADJUSTABLE keyword.

I haven't seen any good reason for this change; the only argument offered
is an argument that would forbid all extensions of any kind -- the argument
is that any program that uses an extension cannot be ported to an
implementation that lacks the extension.

I mildly favor ADJUST-ARRAY-NOT-ADJUSTABLE:IMPLICIT-COPY, although I
think I would be just as happy with the status quo.