bug#12467: 24.1; customization initialization confusing

[Glenn Morris <rgm@gnu.org>]

BTW, here is the relevant quote from the elisp manual (it's not really
relevant for the Emacs manual IMO):

 -- Function: custom-set-variables &rest args
     This function installs the variable customizations specified by
     ARGS.  Each argument in ARGS should have the form

          (VAR EXPRESSION [NOW [REQUEST [COMMENT]]])

     VAR is a variable name (a symbol), and EXPRESSION is an expression
     which evaluates to the desired customized value.

     If the `defcustom' form for VAR has been evaluated prior to this
     `custom-set-variables' call, EXPRESSION is immediately evaluated,
     and the variable's value is set to the result.  Otherwise,
     EXPRESSION is stored into the variable's `saved-value' property,
     to be evaluated when the relevant `defcustom' is called (usually
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     when the library defining that variable is loaded into Emacs).
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^