Fix int -> machine_int_t; add print to slice test.
diff --git a/py/objstr.c b/py/objstr.c
index 6a0721d..59547e3 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -35,7 +35,7 @@
                 return mp_obj_new_int(lhs_str[mp_obj_get_int(rhs_in)]);
 #if MICROPY_ENABLE_SLICE
             } else if (MP_OBJ_IS_TYPE(rhs_in, &slice_type)) {
-                int start, stop, step;
+                machine_int_t start, stop, step;
                 mp_obj_slice_get(rhs_in, &start, &stop, &step);
                 assert(step == 1);
                 int len = strlen(lhs_str);