pgsql: Modify parallel pg_restore to track pending and ready items by

Log Message:
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Modify parallel pg_restore to track pending and ready items by means of
two new lists, rather than repeatedly rescanning the main TOC list.
This avoids a potential O(N^2) slowdown, although you'd need a *lot*
of tables to make that really significant; and it might simplify future
improvements in the scheduling algorithm by making the set of ready
items more easily inspectable. The original thought that it would
in itself result in a more efficient job dispatch order doesn't seem
to have been borne out in testing, but it seems worth doing anyway.

Modified Files:
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pgsql/src/bin/pg_dump:
pg_backup_archiver.c (r1.174 -> r1.175)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_backup_archiver.c?r1=1.174&r2=1.175)
pg_backup_archiver.h (r1.81 -> r1.82)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_backup_archiver.h?r1=1.81&r2=1.82)