Re: doc elisp intro cross reference fixes

[Luc Teirlinck]

>From my previous message:

   Not only would blindly turning a *-defvar into a
   defcustom be dangerous, it is impossible.  You will have to decide on
   a :group, a :type and so on.

I said this too quickly, defcustom without :group indeed works.  It
just does not show up in a customization buffer (which it should not).

Sincerely,

Luc.