py: Make tuple and list use mp_int_t/mp_uint_t.

Part of code cleanup, to resolve issue #50.
diff --git a/py/objexcept.c b/py/objexcept.c
index c1d0149..6064291 100644
--- a/py/objexcept.c
+++ b/py/objexcept.c
@@ -464,7 +464,7 @@
         *n = 0;
         *values = NULL;
     } else {
-        uint n2;
+        mp_uint_t n2;
         mp_obj_list_get(self->traceback, &n2, (mp_obj_t**)values);
         *n = n2;
     }