Make some messages more consistent

contrib/pg_standby/pg_standby.c

src/backend/access/transam/xlog.c

src/backend/commands/tablespace.c

src/bin/initdb/initdb.c

src/bin/pg_config/pg_config.c

src/bin/pg_ctl/pg_ctl.c

src/interfaces/ecpg/ecpglib/error.c

src/pl/plpython/plpython.c

src/test/regress/pg_regress.c

src/timezone/pgtz.c