Make users of struct cmdstr agree on prototype of member c_addr.

Make users of struct cmdstr agree on prototype of member c_addr.
(player_login): Use player->argp[] to store arguments.
(client_cmd, user_cmd, sanc_cmd, coun_cmd, pass_cmd, play_cmd,
kill_cmd, list_cmd, quit_cmd): Remove parameters, fetch arguments from
player->argp[].
(cmdstr): Prototype member c_addr.

(play_cmd): Used to silently ignore up to two arguments if there
wasn't a third one.  Don't.