fix bug in self-tail-recursion with "external" variables; other sundries

* gdbinit (pp, inst): New commands.

* libguile/vm-engine.c (vm_error_not_a_pair): New error case.

* libguile/vm-i-scheme.c (VM_VALIDATE_CONS): New macro -- use this
  instead of SCM_VALIDATE_* because SCM_VALIDATE will exit nonlocally
  before we have a chance to sync the regs.
  (car, cdr, set-car, set-cdr): Use VM_VALIDATE_CONS.

* libguile/vm-i-system.c (goto/args): Bugfix: when doing a
  self-tail-recursion, allocate fresh externals. Fixes use of match.go.

* module/system/vm/assemble.scm (dump-object!): Add some checks that we
  aren't dumping out values that the VM can't handle.

* module/system/vm/disasm.scm (disassemble-externals): Fix rotten call to
  `print-info'.

* oop/goops/dispatch.scm: Add a FIXME.

* testsuite/Makefile.am (vm_test_files):
* testsuite/t-closure4.scm (extract-symbols): New test, distilled with
  much effort out of match.scm.

* ice-9/Makefile.am (NOCOMP_SOURCES): Re-enable compilation of match.scm.
  Yay!

testsuite/Makefile.am

@@ -11,6 +11,7 @@ vm_test_files =					\
       t-closure.scm				\
       t-closure2.scm				\
       t-closure3.scm				\
+      t-closure4.scm				\
       t-do-loop.scm				\
       t-macros.scm				\
       t-macros2.scm				\

testsuite/t-closure4.scm

@@ -0,0 +1,22 @@
+(define (extract-symbols exp)
+  (define (process x out cont)
+    (cond ((pair? x)
+           (process (car x)
+                    out
+                    (lambda (car-x out)
+                      ;; used to have a bug here whereby `x' was
+                      ;; modified in the self-tail-recursion to (process
+                      ;; (cdr x) ...), because we didn't allocate fresh
+                      ;; externals when doing self-tail-recursion.
+                      (process (cdr x)
+                               out
+                               (lambda (cdr-x out)
+                                 (cont (cons car-x cdr-x)
+                                       out))))))
+          ((symbol? x)
+           (cont x (cons x out)))
+          (else
+           (cont x out))))
+  (process exp '() (lambda (x out) out)))
+
+(extract-symbols '(a b . c))