remove the [ and ] prompt expansions from prompt strings that are not used with readl...

remove the [ and ] prompt expansions from prompt strings that are not used with readline; fix some redisplay issues when readline does not start in column 0; fix memory leak in unquoted $@ expansion; fix readline redisplay issue after SIGWINCH shrinks the terminal size; fix issue with mapfile that can cause crashes if a callback unsets the array mapfile is using