Refactor seclabel.c to use the new check_object_ownership function.
Refactor seclabel.c to use the new check_object_ownership function.

This avoids duplicate (and not-quite-matching) code, and makes the logic
for SECURITY LABEL match COMMENT and ALTER EXTENSION ADD/DROP.

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