Merge from upstream; add version to defvar.

Added line as part of commit 20f57d6a7d4543dabaadd26b94e1c0405d3f802a
  Author:     Stefan Monnier <monnier@iro.umontreal.ca>
  AuthorDate: Mon Sep 29 14:14:08 2014 -0400

      Rename 24.5 to 25.1

      Except where we expect to backport the corresponding change.