Message style fixes

contrib/test_decoding/expected/slot.out

src/backend/access/transam/xlog.c

src/backend/access/transam/xlogfuncs.c

src/backend/catalog/pg_aggregate.c

src/backend/libpq/auth.c

src/backend/replication/basebackup.c

src/backend/replication/slotfuncs.c

src/backend/storage/file/fd.c

src/backend/utils/adt/ri_triggers.c

src/backend/utils/misc/guc.c

src/test/regress/expected/foreign_key.out