External onclick handler for renaming media file.

NOTE: Renaming is not completed, submitting the prompt results in
      an error msg:

"Your browser did not sent a valid HTTP-Referrer string. This may
have either been caused by a misconfigured browser/proxy or by a
Cross Site Request Forgery (XSRF) aimed at you. The action you
requested could not be completed."

      This is beyond my JS knowledge. @onli …?