Replacement of the buffer replacement strategy with an ARC

src/backend/commands/vacuum.c

src/backend/storage/buffer/buf_init.c

src/backend/storage/buffer/buf_table.c

src/backend/storage/buffer/bufmgr.c

src/backend/storage/buffer/freelist.c

src/backend/utils/misc/guc.c

src/backend/utils/misc/postgresql.conf.sample

src/include/miscadmin.h

src/include/storage/buf_internals.h