Re: pg_dump dump catalog ACLs

I've not included it in this patch, but my thinking here would be to add
a check to the GRANT functions which checks 'if (creating_extension)'
and records/updates the entries in pg_init_privs for those objects.
This is similar to how we handle dependencies for extensions currently.
That way, extensions don't have to do anything and if the user changes
the permissions on an extension's object, the permissions for that
object would then be dumped out.

This still requires more testing, documentation, and I'll see about
making it work completely for extensions also, but wanted to provide an
update and solicit for review/comments.

The patches have been broken up in what I hope is a logical way for
those who wish to review/comment:

#1 - Add the pg_init_privs catalog
#2 - Change pg_dump to use a bitmap instead of boolean for 'dump'
#3 - Split 'dump' into 'dump' and 'dump_contains'
#4 - Make pg_dump include changed ACLs in dump of 'pg_catalog'

#5 - Remove 'if (!superuser()) ereport()' calls and REVOKE EXECUTE