Fix to prevent too large tuple from being created.

src/backend/access/heap/stats.c

src/backend/catalog/index.c

src/backend/commands/copy.c

src/backend/commands/vacuum.c

src/backend/optimizer/path/_deadcode/xfunc.c

src/backend/parser/gram.y

src/backend/storage/page/bufpage.c

src/backend/utils/adt/varchar.c

src/include/access/htup.h

src/include/storage/bufpage.h

src/interfaces/ecpg/preproc/preproc.y