core: Fix printing bindings.

* src/lib.c (car_): Support taking the car of a binding.
* mes/module/mes/display.mes (display): Do not use 'list->string'
when displaying a binding.

mes/module/mes/display.mes

@@ -125,7 +125,7 @@
         (display ">" port))
        ((binding? x)
         (display "#<binding " port)
-        (write (list->string (car (core:car x))) port)
+        (write (car (core:car x)) port)
         (display ">" port))
        ((number? x)
         (display (number->string x) port))

src/lib.c

@@ -39,7 +39,7 @@ struct scm *
 car_ (struct scm *x)
 {
   struct scm *a = x->car;
-  if (x->type == TPAIR)
+  if (x->type == TPAIR || x->type == TBINDING)
     return a;
   return make_number (cast_scmp_to_long (a));
 }