While customizing savehist mode through the emacs Custom interface, I
discovered that I could not set `savehist-autosave-interval' to nil
because the custom buffer only had an integer entry field for that
variable, although the docstring said that nil was a valid value. So I
edited the custom definition to allow choosing either nil or an integer,
instead of just an integer. I also added labels to the two choices to
make things clearer for the user. Here is the one-line diff (assuming
that it doesn't get too badly mangled in transit):

BEGIN DIFF
*** old/savehist.el    2009-11-26 21:47:52.378311830 -0800
--- new/savehist.el    2009-11-26 21:19:12.118518476 -0800
***************
*** 120,126 ****
  (defcustom savehist-autosave-interval (* 5 60)
    "The interval between autosaves of minibuffer history.
  If set to nil, disables timer-based autosaving."
!   :type 'integer
    :group 'savehist)

  (defcustom savehist-mode-hook nil
--- 120,127 ----
  (defcustom savehist-autosave-interval (* 5 60)
    "The interval between autosaves of minibuffer history.
  If set to nil, disables timer-based autosaving."
!   :type '(choice (const :tag "Disabled" nil)
!                  (integer :tag "Seconds" 300))
    :group 'savehist)

  (defcustom savehist-mode-hook nil
END DIFF

Here is my attempt at manually writing a changelog entry:

BEGIN CHANGELOG
     2009-11-62  Ryan C. Thompson  <rct@thompsonclan.org>

             * savehist.el: Allow setting `savehist-autosave-interval'
               to nil in Custom.
END CHANGELOG

If it matters, you have my blessing to license this code however you please.

- Ryan Thompson