In pg_dump, use a bitmap to represent what to include

pg_dump has historically used a simple boolean 'dump' value to indicate
if a given object should be included in the dump or not.  Instead, use
a bitmap which breaks down the components of an object into their
distinct pieces and use that bitmap to only include the components
requested.

This does not include any behavioral change, but is in preperation for
the change to dump out just ACLs for objects in pg_catalog.

Reviews by Alexander Korotkov, Jose Luis Tallon