Structure redefinition warning for closure-common

[mevenson]

From <​https://github.com/armedbear/abcl/issues/59>:

<​https://github.com/mcna/closure-common> fails to load properly because the xstream structure causes a redefinition failure, the reason being that the slot buffer of type (simple-array buffer-byte (*)) (which is also what's in the FASL, (#5=SYSTEM::DEFSTRUCT-SLOT-DESCRIPTION BUFFER #6=0 XSTREAM-BUFFER +NULL-BUFFER+ (#7=SIMPLE-ARRAY BUFFER-BYTE (#8=*)) #2# )) has the expanded type (SIMPLE-ARRAY (INTEGER 0 65535) (*)) loaded in the runtime (c.f. (nth 0 (system::dd-slots (get 'runes::xstream 'system::structure-definition)))).

Structure redefinition not supported in DEFSTRUCT for XSTREAM
   [Condition of type PROGRAM-ERROR]

Restarts:
 0: [TRY-RECOMPILING] Recompile xstream and try loading it again
...
Backtrace:
...
  4: (ERROR PROGRAM-ERROR :FORMAT-CONTROL "Structure redefinition not supported ~
                                   in DEFSTRUCT for ~A" :FORMAT-ARGUMENTS (RUNES:XSTREAM))
  5: (SYSTEM:COMPILER-DEFSTRUCT RUNES:XSTREAM :CONC-NAME #:XSTREAM- :DEFAULT-CONSTRUCTOR RUNES::MAKE-XSTREAM/LOW ...)