#Emacs のウィンドウ切り替えについての良スレを見つけた：Emacs, switch to previous window - Stack Overflow
ぼくの .emacs のウィンドウ切り替えキー設定：
(global-set-key "\C-\M-o" 'other-frame)
(defun prev-window ()
(interactive)
(other-window -1))
(global-set-key "\M-o" 'other-window)
(global-set-key "\M-O" 'prev-window)
(global-set-key (kbd "C-x <up>") 'windmove-up)
(global-set-key (kbd "C-x <down>") 'windmove-down)
(global-set-key (kbd "C-x <right>") 'windmove-right)
(global-set-key (kbd "C-x <left>") 'windmove-left)