Add pg_dump support for the new PARALLEL option for aggregates.
Add pg_dump support for the new PARALLEL option for aggregates.

This was an oversight in commit 41ea0c23761ca108e2f08f6e3151e3cb1f9652a1.

Fabrízio de Royes Mello, per a report from Tushar Ahuja

ashwinstar/gpdb,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,xinzweb/gpdb,xinzweb/gpdb,adam8157/gpdb,jmcatamney/gpdb,50wu/gpdb,50wu/gpdb,ashwinstar/gpdb,xinzweb/gpdb,ashwinstar/gpdb,50wu/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,lisakowen/gpdb,lisakowen/gpdb,lisakowen/gpdb,lisakowen/gpdb,lisakowen/gpdb,lisakowen/gpdb,xinzweb/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,adam8157/gpdb,adam8157/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,xinzweb/gpdb,adam8157/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,50wu/gpdb,50wu/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,adam8157/gpdb,50wu/gpdb,greenplum-db/gpdb,adam8157/gpdb,50wu/gpdb,adam8157/gpdb,adam8157/gpdb,jmcatamney/gpdb