Which version of Texinfo do we require?

[John Wiegley]

I tried building elisp.pdf in emacs-25, and the build failed on line 560 of
frames.texi:

    @itemize @w

Changing it to "@w{}" causes the build to go through. I'm using texinfo 6.0.
The docs say:

  "If you don’t specify a mark command, the default is @bullet. If you don’t
  want any mark at all, but still want logical items, use @w{} (in this case
  the braces are required)."

In this a bug, or is it my version of Texinfo?

John