It seems most IMAP4 methods accept str as arguments right now (I
checked: list, lsub, myrights, select, status, search, fetch) and
login() is a sole exception. I know the protocol is mostly ascii only,
but still having possibility of using str in the API feels convenient
and reasonable to me. Can't we convert str parameters to login() to
ascii too? It already done in other methods (the _command() method
iterates over args and converts them).