Serialized mode works!

src/backend/access/transam/transam.c

src/backend/access/transam/xact.c

src/backend/executor/execMain.c

src/backend/storage/ipc/shmem.c

src/backend/storage/lmgr/lmgr.c

src/backend/tcop/postgres.c

src/backend/utils/time/tqual.c

src/include/access/transam.h

src/include/utils/tqual.h