Fix systable_recheck_tuple() for MVCC scan snapshots.
Fix systable_recheck_tuple() for MVCC scan snapshots.

Since this function assumed non-MVCC snapshots, it broke when commit
568d4138c646cd7cd8a837ac244ef2caf27c6bb8 switched its one caller from
SnapshotNow scans to MVCC-snapshot scans.

Reviewed by Robert Haas, Tom Lane and Andres Freund.

jmcatamney/gpdb,ashwinstar/gpdb,oberstet/postgres-xl,pavanvd/postgres-xl,xinzweb/gpdb,xinzweb/gpdb,Postgres-XL/Postgres-XL,50wu/gpdb,lisakowen/gpdb,adam8157/gpdb,zeroae/postgres-xl,lisakowen/gpdb,ashwinstar/gpdb,yazun/postgres-xl,50wu/gpdb,yazun/postgres-xl,greenplum-db/gpdb,jmcatamney/gpdb,lisakowen/gpdb,zeroae/postgres-xl,oberstet/postgres-xl,ovr/postgres-xl,50wu/gpdb,oberstet/postgres-xl,50wu/gpdb,xinzweb/gpdb,zeroae/postgres-xl,lisakowen/gpdb,techdragon/Postgres-XL,50wu/gpdb,50wu/gpdb,techdragon/Postgres-XL,jmcatamney/gpdb,50wu/gpdb,jmcatamney/gpdb,xinzweb/gpdb,ovr/postgres-xl,lisakowen/gpdb,pavanvd/postgres-xl,yazun/postgres-xl,adam8157/gpdb,50wu/gpdb,oberstet/postgres-xl,zeroae/postgres-xl,ashwinstar/gpdb,adam8157/gpdb,ashwinstar/gpdb,pavanvd/postgres-xl,ovr/postgres-xl,xinzweb/gpdb,greenplum-db/gpdb,lisakowen/gpdb,lisakowen/gpdb,Postgres-XL/Postgres-XL,techdragon/Postgres-XL,zeroae/postgres-xl,jmcatamney/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,xinzweb/gpdb,ashwinstar/gpdb,techdragon/Postgres-XL,jmcatamney/gpdb,yazun/postgres-xl,greenplum-db/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,ovr/postgres-xl,greenplum-db/gpdb,yazun/postgres-xl,lisakowen/gpdb,adam8157/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,adam8157/gpdb,xinzweb/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,Postgres-XL/Postgres-XL,adam8157/gpdb,greenplum-db/gpdb,pavanvd/postgres-xl,ovr/postgres-xl,pavanvd/postgres-xl,techdragon/Postgres-XL,xinzweb/gpdb,adam8157/gpdb,Postgres-XL/Postgres-XL,oberstet/postgres-xl,Postgres-XL/Postgres-XL,adam8157/gpdb