DEFCLASS fails to signal an ERROR when inheriting from T.

[Jean-Philippe Paradis]

What I do and what happens:
(defclass foo (t)
  ())
=> #<STANDARD-CLASS FOO>

What I expected to happen:
An error getting thrown at compile-time, or perhaps runtime.

Analysis:
From CLHS BUILT-IN-CLASS:
"Attempting to use defclass to define subclasses of a built-in class signals an error of type error."

SBCL version: 1.0.51
uname -a: Linux dynamorph 2.6.32-33-generic #72-Ubuntu SMP Fri Jul 29 21:08:37 UTC 2011 i686 GNU/Linux

*features*:
(:SWANK :QUICKLISP :SB-BSD-SOCKETS-ADDRINFO :ASDF2 :ASDF :ASDF-UNIX :ANSI-CL
 :COMMON-LISP :SBCL :SB-DOC :SB-TEST :SB-LDB :SB-PACKAGE-LOCKS :SB-UNICODE
 :SB-EVAL :SB-SOURCE-LOCATIONS :IEEE-FLOATING-POINT :X86 :UNIX :ELF :LINUX
 :SB-THREAD :LARGEFILE :GENCGC :STACK-GROWS-DOWNWARD-NOT-UPWARD
 :C-STACK-IS-CONTROL-STACK :COMPARE-AND-SWAP-VOPS :UNWIND-TO-FRAME-AND-CALL-VOP
 :RAW-INSTANCE-INIT-VOPS :STACK-ALLOCATABLE-CLOSURES :STACK-ALLOCATABLE-VECTORS
 :STACK-ALLOCATABLE-LISTS :STACK-ALLOCATABLE-FIXED-OBJECTS :ALIEN-CALLBACKS
 :CYCLE-COUNTER :INLINE-CONSTANTS :MEMORY-BARRIER-VOPS :MULTIPLY-HIGH-VOPS
 :LINKAGE-TABLE :OS-PROVIDES-DLOPEN :OS-PROVIDES-DLADDR :OS-PROVIDES-PUTWC
 :OS-PROVIDES-SUSECONDS-T :OS-PROVIDES-GETPROTOBY-R :OS-PROVIDES-POLL)

[Christophe Rhodes (csr21-cantab)]

I worked a bit on this. I didn't really like the separation between implementation (able to perform magic subclassing) and
user (not able to), so I've gone a different way, by defining a new SYSTEM-CLASS metaclass as an interposing superclass
of BUILT-IN-CLASS. I think this meets the requirements, though it does somewhat make a mockery of the "easy" tag. Comments?

[Nick Levine (ndl)]

> Date: Tue, 29 Apr 2014 12:12:34 -0000
> From: Christophe Rhodes <email address hidden>
>
> I worked a bit on this. I didn't really like the separation between
> implementation (able to perform magic subclassing) and user (not
> able to), so I've gone a different way, by defining a new
> SYSTEM-CLASS metaclass as an interposing superclass of
> BUILT-IN-CLASS. I think this meets the requirements, though it does
> somewhat make a mockery of the "easy" tag. Comments?

Only "sorry for taking a month to reply". Anyway I see you submitted
your fix now.

If I ever have time to remind myself what and how SBCL is, and if
nobody else got there first, I'll take a look at 1184325.

- nick