How to avoid pop-up of *Async Shell Command* buffer in Emacs?

Question

My ~/.emacs contains the following settings for opening certain files with certain applications (Ubuntu 12.10; Emacs 24):

(setq dired-guess-shell-alist-user
      '(("\\.pdf\\'" "okular ? &")
    ("\\.djvu\\'" "okular ? &")
        ("\\.mp3\\'" "vlc ? &")
    ("\\.mp4\\'" "vlc ? &")
    ))

When I navigate to a .pdf in dired-mode and hit !, it opens the .pdf in Okular, but the dired-buffer is split into two parts, the second one now being a useless *Async Shell Command* buffer containing content like

okular(25393)/kdecore (KConfigSkeleton) KCoreConfigSkeleton::writeConfig:
okular(25393)/kdecore (KConfigSkeleton) KCoreConfigSkeleton::writeConfig:
okular(25393)/kdecore (KConfigSkeleton) KCoreConfigSkeleton::writeConfig:
okular(25393)/kdecore (KConfigSkeleton) KCoreConfigSkeleton::writeConfig:

How can I prevent this buffer from being opened? (except for, maybe, if there was an error and this information is useful).

I found related questions here and here, but they seem to deal with specific commands executed asynchronously, instead of the *Async Shell Command* in general (if possible, I would like to change the behaviour in general for asynchronous processes, not only for certain file types)

Answer 1

Found this here:

(call-process-shell-command "okular&" nil 0)

Works for me. No stderr gobbledygook.