Replace nested ifs with cond

Replace nested ifs with cond

* lisp/play/dunnet.el (dun-messages, dun-describe-room, dun-examine):
(dun-eat, dun-put-objs, dun-turn, dun-press, dun-ls, dun-cd): Use when
and cond where appropriate.
(dun-sauna-heat): Accept sauna level as an argument.  Use cond.
(dun-take): Use null and dun-mprincl.
(dun-inven-weight, dun-load-d): Reformat.
(dun-remove-obj-from-inven, dun-remove-obj-from-room): Nix setq to nil.