Fix bugs in information_schema.referential_constraints view.
Fix bugs in information_schema.referential_constraints view.

This view was being insufficiently careful about matching the FK constraint
to the depended-on primary or unique key constraint.  That could result in
failure to show an FK constraint at all, or showing it multiple times, or
claiming that it depended on a different constraint than the one it really
does.  Fix by joining via pg_depend to ensure that we find only the correct
dependency.

Back-patch, but don't bump catversion because we can't force initdb in back
branches.  The next minor-version release notes should explain that if you
need to fix this in an existing installation, you can drop the
information_schema schema then re-create it by sourcing
$SHAREDIR/information_schema.sql in each database (as a superuser of
course).

50wu/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,pavanvd/postgres-xl,50wu/gpdb,zeroae/postgres-xl,arcivanov/postgres-xl,zeroae/postgres-xl,kmjungersen/PostgresXL,zeroae/postgres-xl,greenplum-db/gpdb,snaga/postgres-xl,adam8157/gpdb,postmind-net/postgres-xl,arcivanov/postgres-xl,50wu/gpdb,adam8157/gpdb,tpostgres-projects/tPostgres,adam8157/gpdb,lisakowen/gpdb,50wu/gpdb,lisakowen/gpdb,snaga/postgres-xl,50wu/gpdb,adam8157/gpdb,arcivanov/postgres-xl,postmind-net/postgres-xl,pavanvd/postgres-xl,ovr/postgres-xl,snaga/postgres-xl,ashwinstar/gpdb,techdragon/Postgres-XL,Postgres-XL/Postgres-XL,arcivanov/postgres-xl,yazun/postgres-xl,Postgres-XL/Postgres-XL,yazun/postgres-xl,yazun/postgres-xl,yazun/postgres-xl,techdragon/Postgres-XL,xinzweb/gpdb,postmind-net/postgres-xl,ashwinstar/gpdb,jmcatamney/gpdb,kmjungersen/PostgresXL,postmind-net/postgres-xl,jmcatamney/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,tpostgres-projects/tPostgres,adam8157/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,lisakowen/gpdb,lisakowen/gpdb,Postgres-XL/Postgres-XL,Postgres-XL/Postgres-XL,snaga/postgres-xl,ovr/postgres-xl,arcivanov/postgres-xl,xinzweb/gpdb,ovr/postgres-xl,postmind-net/postgres-xl,oberstet/postgres-xl,xinzweb/gpdb,kmjungersen/PostgresXL,zeroae/postgres-xl,techdragon/Postgres-XL,jmcatamney/gpdb,adam8157/gpdb,greenplum-db/gpdb,oberstet/postgres-xl,techdragon/Postgres-XL,50wu/gpdb,tpostgres-projects/tPostgres,pavanvd/postgres-xl,lisakowen/gpdb,jmcatamney/gpdb,adam8157/gpdb,xinzweb/gpdb,greenplum-db/gpdb,oberstet/postgres-xl,arcivanov/postgres-xl,oberstet/postgres-xl,tpostgres-projects/tPostgres,greenplum-db/gpdb,oberstet/postgres-xl,ovr/postgres-xl,techdragon/Postgres-XL,ovr/postgres-xl,Postgres-XL/Postgres-XL,adam8157/gpdb,kmjungersen/PostgresXL,tpostgres-projects/tPostgres,lisakowen/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,yazun/postgres-xl,ashwinstar/gpdb,lisakowen/gpdb,50wu/gpdb,pavanvd/postgres-xl,pavanvd/postgres-xl,kmjungersen/PostgresXL,ashwinstar/gpdb,50wu/gpdb,jmcatamney/gpdb,xinzweb/gpdb,lisakowen/gpdb,snaga/postgres-xl,xinzweb/gpdb,zeroae/postgres-xl,xinzweb/gpdb,xinzweb/gpdb,ashwinstar/gpdb