Add tests for sequence privileges
Minimize calls of pg_class_aclcheck to minimum necessary

In a couple of code paths, pg_class_aclcheck is called in succession
with multiple different modes set.  This patch combines those modes to
have a single call of this function and reduce a bit process overhead
for permission checking.

Author: Michael Paquier <michael@otacoo.com>
Reviewed-by: Fabrízio de Royes Mello <fabriziomello@gmail.com>