Backends reflect "GRANT role_name" changes rather quickly, due to a syscache
invalidation callback. Let's register an additional callback to reflect
"ALTER ROLE ... [NO]INHERIT" with equal speed. I propose to back-patch this.
While pg_authid changes may be more frequent than pg_auth_members changes, I
expect neither is frequent enough to worry about the resulting acl.c cache
miss rate.
pg_authid changes don't affect cached_membership_roles, so I could have
invalidated cached_privs_roles only. That felt like needless complexity. I
expect cached_privs_role gets the bulk of traffic, since SELECT, INSERT,
UPDATE and DELETE use it. cached_membership_roles pertains to DDL and such.
