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!

gdbinit

@@ -1,7 +1,13 @@
+# -*- GDB-Script -*-
+
 define newline
   call (void)scm_newline (scm_current_error_port ())
 end
 
+define pp
+  call (void)scm_call_1 (scm_variable_ref (scm_c_module_lookup (scm_c_resolve_module ("ice-9 pretty-print"), "pretty-print")), $arg0)
+end
+
 define gdisplay
   call (void)scm_display ($arg0, scm_current_error_port ())
   newline
@@ -194,3 +200,7 @@ define vmstack
     nextframe
   end
 end
+
+define inst
+  p scm_instruction_table[$arg0]
+end