remove before-signal-stack

* module/ice-9/boot-9.scm (before-signal-stack): Remove. We're moving
  away from using the-last-stack, so this backup copy is not much use.
  (top-repl): Don't bother saving a before-signal-stack.

* module/ice-9/debugger/command-loop.scm (debugger-handler): No need to
  restore here either.

module/ice-9/boot-9.scm

@@ -2690,7 +2690,6 @@ module '(ice-9 q) '(make-q q-length))}."
   (restore-signals))
 
 ;;(define the-last-stack (make-fluid)) Defined by scm_init_backtrace ()
-(define before-signal-stack (make-fluid))
 ;; FIXME: stack-saved? is broken in the presence of threads.
 (define stack-saved? #f)
 
@@ -3460,9 +3459,6 @@ module '(ice-9 q) '(make-q q-length))}."
           (lambda ()
             (let ((make-handler (lambda (msg)
                                   (lambda (sig)
-                                    ;; Make a backup copy of the stack
-                                    (fluid-set! before-signal-stack
-                                                (fluid-ref the-last-stack))
                                     (save-stack 2)
                                     (scm-error 'signal
                                                #f

module/ice-9/debugger/command-loop.scm

@@ -1,6 +1,6 @@
 ;;;; Guile Debugger command loop
 
-;;; Copyright (C) 1999, 2001, 2002, 2003, 2006 Free Software Foundation, Inc.
+;;; Copyright (C) 1999, 2001, 2002, 2003, 2006, 2010 Free Software Foundation, Inc.
 ;;;
 ;;;; This library is free software; you can redistribute it and/or
 ;;;; modify it under the terms of the GNU Lesser General Public
@@ -45,8 +45,6 @@
   (case key
     ((exit-debugger) #f)
     ((signal)
-     ;; Restore stack
-     (fluid-set! the-last-stack (fluid-ref before-signal-stack))
      (apply display-error #f (current-error-port) args))
     (else
      (display "Internal debugger error:\n")