Message wording and pluralization improvements

src/backend/access/transam/xlog.c

src/backend/bootstrap/bootstrap.c

src/bin/pg_basebackup/pg_basebackup.c

src/bin/pg_basebackup/pg_receivewal.c

src/bin/pg_basebackup/streamutil.c

src/bin/pg_controldata/pg_controldata.c

src/bin/pg_resetwal/pg_resetwal.c

src/bin/pg_rewind/pg_rewind.c

src/bin/pg_upgrade/pg_upgrade.c

src/bin/pg_waldump/pg_waldump.c