optimized constructors don't see constant redefinitions

[3b]

from _death on #lisp (http://paste.lisp.org/display/332457)

CL-USER> (defconstant meaning-of-universe 41)
MEANING-OF-UNIVERSE
CL-USER> (defclass encapsulated ()
           ((thing :initarg :thing :reader thing)))
#<STANDARD-CLASS COMMON-LISP-USER::ENCAPSULATED>
CL-USER> (defun encapsulate ()
           (make-instance 'encapsulated
                          :thing meaning-of-universe))
ENCAPSULATE
CL-USER> (thing (encapsulate))
41
CL-USER> (defconstant meaning-of-universe 42) ;; pick 'continue' restart
MEANING-OF-UNIVERSE
CL-USER> meaning-of-universe
42
CL-USER> (defun encapsulate ()
           (make-instance 'encapsulated
                          :thing meaning-of-universe))
WARNING: redefining COMMON-LISP-USER::ENCAPSULATE in DEFUN
ENCAPSULATE
CL-USER> (thing (encapsulate))
41
CL-USER> (lisp-implementation-version)
"1.3.11"

While redefining the constant is technically non-conformant, not seeing the new definition in a function compiled after the redefinition makes the continue restart less useful.

from #sbcl:

<scymtym> from a brief look, the MAKE-INSTANCE gets an optimized constructor
          which is cached with the constant symbol as part of the key, leading
          to the redefined function getting the same constructor [19:52]