> It works fine, but if longlines-mode is active, then when file is been
 > modified by external program, I get not only my message, but before it I
 > get question in minibuffer "filename.txt changed on disk; really edit
 > the buffer? (y, n, r or C-h)". Why? I want only my message. How to
 > disable this question?

Can you try the attached patch?   It's against CVS Emacs hence
if you have any problems applying it please tell me.