refine "unknown data type" message.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@9700 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

gc.c

@@ -974,9 +974,9 @@ gc_mark_children(VALUE ptr, int lev)
 	break;
 
       default:
-	rb_bug("rb_gc_mark(): unknown data type 0x%lx(%p) %s",
+	rb_bug("rb_gc_mark(): unknown data type 0x%lx (%p) %s",
 	       obj->as.basic.flags & T_MASK, obj,
-	       is_pointer_to_heap(obj) ? "corrupted object" : "non object");
+	       is_pointer_to_heap(obj) ? "corrupted object" : "not a pointer to heap");
     }
 }